Die polymerisation der lactame XI. Die copolymerisation von 6-caprolactam mit 12-laurolactam

The course of the incorporation of 6-caprolactam and 12-laurolactam into polymer chains during the hydrolytic, cationic and anionic copolymerization for an equimolar ratio of the monomers was studied. During the hydrolytic copolymerization 6-caprolactam is incorporated more rapidly at 260, 230 or 200°C at the beginning of the polymerization process; the differences between incorporation rates of the lactams into the copolymer increase with decreasing temperature. During the cationic copolymerization the incorporation of 12-laurolactam is more rapid by orders of magnitude for the above temperatures at the beginning of the process. Changes in the composition of cationic copolymers as compared to the hydrolytic copolymers are independent of the temperature during the copolymerization. The anionic copolymerization is characterized by a more rapid incorporation of 6-caprolactam into the polymer chain. The differences in the polymerization activity of the two lactams decrease with increasing temperature of the anionic copolymerization. The described course of incorporation of individual monomers, with the various mechanisms of the polymerization, also corresponds to melting points of copolymers in accordance with their composition.     

Flame retardancy afforded by polyaniline deposited on wood

Wood scantlings were coated with polyaniline (PANI) during the in situ polymerization of aniline with ammonium peroxydisulfate in an aqueous medium. The coating was made in hydrochloric or phosphoric acid solutions in both the absence and presence of stabilizers, poly(N‐vinylpyrrolidone) or colloidal silica. The PANI‐coated wood was placed in a flame or in a furnace operating at 400 or 600°C, and the decrease in the mass was determined. The wood coated with PANI was less reduced in its mass than uncoated samples and was converted to charcoal rather than to ashes. The deposition of related polymers, polypyrrole and poly(1,4‐phenylenediamine), provided similar protection against heat exposure. Fourier transform infrared and Raman spectra of the residues after the burning of PANI‐coated wood were compared. The soaking of wood in PANI colloids did not result in similar protection of wood against fire; the coating of the cellulose fibers with PANI during the polymerization was needed for the enhanced stability of wood at elevated temperatures. The concept of carbonization processes at the surface layer of PANI‐coated cellulose fibers leading to the formation of carbonaceous microtubes is offered to explain the improved stability of wood against flame and heat exposure. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 103: 24–30, 2007     

Microwave and Terahertz Surface Resistance of MgB2 Thin Films

The knowledge of the surface resistance R _s of superconducting thin film at microwave and terahertz (THz) regions is significant to design, make and assess superconducting microwave and THz electronic devices. In this paper we reported the R _s of MgB₂ films at microwave and THz measured with sapphire resonator technique and the time-domain THz spectroscopy, respectively. Some interesting results are revealed in the following: (1) A clear correlation is found between R _s and normal-state resistivity right above T _c, ρ₀, i.e., R _s decreases almost linearly with the decrease of ρ₀. (2) A low residual R _s, less than 50 μΩ at 18 GHz is achieved by different deposition techniques. In addition, between 10 and 14 K, MgB₂ has the lowest R _s compared with two other superconductors Nb₃Sn and the high-temperature superconductor YBa₂Cu₃O_7−δ(YBCO). (3) From THz measurement it is found that the R _s of MgB₂ up to around 1 THz is lower than that of copper and YBCO at the temperature below 25 K. (4) The frequency dependence of R _s follows ω ⁿ , where ω is angular frequency, and n is power index. However, n changes from 1.9 at microwave to 1.5 at THz. The above results clearly give the evidences that MgB₂ thin film, compared with other superconductors, is of advantage to make superconducting circuits working in the microwave and THz regions.     

CAVE: A package for detection and quantitative analysis of internal cavities in a system of overlapping balls: Application to proteins

We developed a software package (CAVE) in Fortran language to detect internal cavities in proteins which can be applied also to an arbitrary system of balls. The volume, the surface area and other quantitative characteristics of the cavities can be calculated. The code is based on the recently suggested enveloping triangulation algorithm [J. Buša et al., J. Comp. Chem. 30 (2009) 346] for computing volume and surface area of the cavity by analytical equations. Different standard sets of atomic radii can be used. The PDB compatible file containing the atomic coordinates must be stored on the disk in advance. Testing of the code on different proteins and artificial ball systems showed efficiency and accuracy of the algorithm. The program is fast. It can handle a system of several thousands of balls in the order of seconds on contemporary PC's. The code is open source and free.

Program summary

Program title: CAVECatalogue identifier: AEHC_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEHC_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 8670No. of bytes in distributed program, including test data, etc.: 100 131Distribution format: tar.gzProgramming language: FortranComputer: PC Pentium and CoreOperating system: Linux system and Windows XP systemClassification: 16.1Nature of problem: Molecular structure analysis.Solution method: Analytical method for cavities detection, and numerical algorithm for volume and surface area calculation based on the analytical formulas, after using the stereographic transformation.Running time: Depends on the size of the molecule under consideration. The test example included in the distribution takes about 1 minute to run.     

BDDC by a frontal solver and the stress computation in a hip joint replacement

A parallel implementation of the Balancing Domain Decomposition based on Constraints (BDDC) method using the frontal solver is employed to solve systems of linear equations from finite element analysis, and incorporated into a standard finite element system for engineering analysis by linear elasticity. Results of computation of stress in a hip replacement are presented. The part is made of titanium and loaded by the weight of human body. The performance of BDDC with added constraints by averages and with added corners is compared.     

Flow characterization in T-shaped and cross-shaped micromixers

The understanding of physical phenomena such as flow behaviour and mass transfer performance is needed in order to develop appropriate micromixers for industrial or biomedical applications. In this article, the flow behaviour of the T-shaped and the cross-shaped micromixers with square cross-section are studied through numerical and experimental investigations. The comparisons are based on identical treated fluxes. From the particle image velocimetry (PIV) measurements, the flow topologies in the T-shaped and cross-shaped micromixers are very different. After liquid impact, it is observed that the vortex structures cover a longer part of the outlet channel in the case of the cross geometry. This result indicates that the cross-shaped micromixer could improve the mixing process in comparison with the micromixers having T geometry. A second experimental technique has been used, the electrochemical one, involving microelectrodes placed at several wall positions of the cross-shaped micromixer. The electrochemical method can locally characterize the formation of swirling flows. The high values of wall shear rate, in the impact zone, confirm the near wall disturbance created by the impingement of the flow and also the appearance of vortices that could enhance fluid mixing.     

Implant Evaluation of a Nuclear Power Source? Betacel? Battery

In order to evaluate nuclear power sources for biomedical applications, a nuclear battery, Betacel?, was used to power two telemetry transmitters designed with a very low power consumption. The transmitters were implanted in a dog to measure the voltage of the battery and the deep body temperature. Special care was given to the glass packaging to prevent possible damage from body fluids. The experiment ran continuously for a 6-month period before termination. At that time, the animal was sacrificed to examine the radiation damage of tissues in the vicinity of the transmitters as well as the effects on vital organs. No measurable abnormality was detected. The experiment suggests that the nuclear power source can be used to extend the working life of implanted medical instruments.     

Thermodynamics of the liquid Co-Cu system and calculation of phase diagram

Knudsen-cell mass spectrometric measurements have been carried out in the liquid phase of the Co-Cu system in the concentration range 25.0 to 85.9 at. % Cu in the temperature range 1347 to 1587 °C. The molar excess Gibbs energy, enthalpy and entropy of mixing, as well as the thermodynamic activities of components in the liquid Co-Cu system were determined using the composition and temperature dependence of the ratio of intensities of ⁵⁹Co and ⁶³Cu ions. The results show that a subregular solution model would fit measured data well (2-parameter thermodynamically adapted power (TAP) series: C _n ^H in J·mol⁻¹; C ₁ ^H =35,961, C ₂ ^H =−5573.2; C _n ^S in J·mol^−1·K−1; C ₁ ^S =5.54, C ₂ ^S =−3.35). A special experiment verified solid-liquid phase equilibrium at 1327 °C and the phase diagram was calculated.     

Duplex surface treatment of stainless steel X12CrNi 18 8

Described technology of stainless steel duplex surface treatment is based on the plasma nitriding of the component in micropulse plasma and subsequent coating by Ni and composite Ni/diamond film. The formed duplex coating is characterized by very good mechanical properties, e.g., an excellent abrasion resistance, a low friction coefficient and a high hardness. __________ Translated from Problemy Prochnosti, No. 1, pp. 129–132, January–February, 2008.