Water soluble acrylamide polymers, 2. Aging and viscous flow of aqueous solutions of polyacrylamide and hydrolyzed polyacrylamide

The aging of aqueous solutions of polyacrylamide which appears experimentally as a decrease of solution viscosity and which is probably caused by microorganisms may be prevented by the addition of a small amount (0.02 wt.-%) of an antimicrobial agent such as sodium azide. Aluminium chloride causes a very strong decrease of the viscosity during a prolongated storing time. The addition of aluminium ions to the polymer solution leads to a complexing of amidic groups with aluminium cations and probably also to decrease of the dimensions of individual polymer coils. The viscous flow of aqueous solutions of polyacrylamide and hydrolyzed polyacrylamides was studied as a dependence of the shear gradient D on the shear stress τ and was described by the relation D = k · τⁿ, where k and n denote constants. Both constants depend on the polymer concentration, the degree of polymerization and the content of carboxylic groups in the polymer. The greatest deviations from the Newtonian behaviour were found in the range of molecular weights over 2 · 10⁶ g/mol and practically no deviations were observed for polyacrylamide with molecular weights below 1 · 10⁶ g/mol. The dependence of the viscosity on the shearing time at different shear rates (300, 600 and 1200 s^?1) which was observed in solutions of polyacrylamide, hydrolyzed polyacrylamide and poly-(N,N-dimethyl)-acrylamide was explained by an entanglement model.     

Influence of TiO2 nanoparticles on nonisothermal crystallization of PP in a wide range of cooling rates analyzed by fast scanning DSC

The influence of titanium dioxide (TiO₂) nanoparticles on the crystallization behavior of polypropylene was investigated by conventional differential scanning calorimetry (DSC) and fast scanning DSC measurements. The data obtained from both methods were estimated for the first time using the Lauritzen‐Hoffmann equation to analyze the behavior over a wide cooling range under nonisothermal conditions. This provides more reliable values of nucleation parameters (K_g) and surface free energy (σ_e). The variation of the effective energy (ΔE) was determined with the Kissinger method. Regardless of the cooling rate, both K_g and σ_e indicate the role of titania as a nucleating agent enhances the crystallization rate. However, the ΔE denotes that TiO₂ acts as an obstacle to the mobility of chain segments at cooling rates below 150 °C/s, while, in contrast, the presence of titania enhances the chain mobility at cooling rates above 150 °C/s. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43944.     

Controllable Broadband Absorption in the Mixed Phase of Metamagnets

Materials with broad absorption bands are highly desirable for electromagnetic filtering and processing applications, especially if the absorption can be externally controlled. Here, a new class of broadband‐absorption materials is introduced. Namely, layered metamagnets exhibit an electromagnetic excitation continuum in the magnetic‐field‐induced mixed ferro‐ and anti­ferromagnetic phase. Employing a series of complementary experimental techniques involving neutron scattering, muon spin relaxation, specific heat, ac and dc magnetization measurements, and electron magnetic resonance, a detailed magnetic phase diagram of Cu₃Bi(SeO₃)₂O₂Br is determined and it is found that the excitations in the mixed phase extend over at least ten decades of frequency. The results, which reveal a new dynamical aspect of the mixed phase in metamagnets, open up a novel approach to controllable microwave filtering.     

Evaluation of non-linear strain paths using Generalized Forming Limit Concept and a modification of the Time Dependent Evaluation Method

The prediction of formability is one of the most important tasks in sheet metal forming process simulation. The common criterion for ductile fracture in industrial applications is the Forming Limit Diagram (FLD). This is only applicable for linear strain paths. However, in most industrial simulation cases non-linear strain paths occur. To resolve this problem, a phenomenological approach is introduced, the so-called Generalized Forming Limit Concept (GFLC). The GFLC enables prediction of localized necking on arbitrary non-linear strain paths. Another possibility is the use of the Time Dependent Evaluation Method (TDEM) within the simulation as a failure criteria. During the Numisheet Benchmark 1 (2014) a two-stage forming process was performed with three typical sheet materials (AA5182, DP600 and TRIP 780) and three different blank shapes. The task was to determinate the point in time and space of local instability. Therefore the strain path for the point of maximum local thinning is evaluated. To predict the start of local necking the Generalized Forming Limit Concept (GFLC), the Time Dependent Evaluation Method (TDEM) and the modified TDEM were applied. The results of the simulation are compared with the results of the Benchmark experiment.     

Energieeffizienz in der Vakuumtechnik

Energy efficiency in vacuum technology Vacuum is used to produce a huge variety of products of our everyday life. To provide the vacuum environment, a lot of energy is usually used and therefore the vacuum pumps should run as efficient as possible. Actually, many various improvements can be made to gain energy savings on vacuum pumps. With those considered in this paper it's possible to save 928 GWh/a of energy in the EU and thereof 629 GWh/a or 64 % are economically realizable. Only specific improvements concerning the vacuum system are taken into account, basic technology options, like motors, controls, etc., are excluded. To show and discuss the results a conserved energy supply curve is used.     

ISIF memories made nonvolatile

Abstract

When scientists discovered the ferroelectric effect more than eighty years ago, they had no idea how these materials would fundamentally revolutionize many aspects of our high-tech activities today.     

Multiparameter microscopy and spectroscopy for single-molecule analytics

The ability to monitor several parameters simultaneously from distinct individual fluorescent reporter molecules facilitates the disentanglement of complex and interacting systems and opens new perspectives in areas from basic science to biopharmaceutical technology. By combining annular illumination microscopy, time-correlated single-photon counting, and multichannel detection, we were able to determine 14 independent parameters from one individual fluorophore. The whole set of parameters was deduced from the few properties of the fluorescence photons, i.e., arrival time, wavelength, and polarization. With this approach, the intensity, the polarization, and the spectral dynamics can be analyzed on a nanosecond time scale and the mean values can be monitored with submillisecond time resolution. Nanosecond spectral dynamics of single molecules has been observed, to the best of our knowledge, for the first time. From our experience, we can determine all parameters for more than 30% of the illuminated fluorophores in biological samples and for more than 80% in doped polymeric films.     

分布式应用中的性能因素

在分布式的场景中,开发者难以理解一次服务调用背后的全部含义。对系统的复杂性理解不足,轻易就会导致资源耗费增加、性能表现下降的结果。