Shear-induced phase separation in cationic surfactant solutions around a rotating sphere

The results of an experimental investigation of the flow of a highly dilute cationic surfactant solution (tetradecyl trimethyl ammonium bromide with added sodium salicylate as counterion, equimolar 2.4mM) around a rotating sphere are presented. The flow and the shear-induced phase transition are visualized by means of a Toepler Schlieren optics. The buildup of the shear-induced structures occurs only above a critical shear rate. Once this critical value is exceeded the shear-induced phase separation starts after a characteristic deformation with the shear rate reduced by the critical one. Further analysis of the obtained data is performed on basis of an analytical calculation of the flow around a rotating sphere in a second order fluid (Thomas and Walters, 1964; Giesekus, 1965). From some characteristic features of the shear-induced structures as induction time and position the parameter describing the elastic properties of the fluid is estimated. Received: 6 January 1998 Accepted: 1 May 1998     

The lattice discrepancy of certain three-dimensional bodies

Based on a very precise approximation to the lattice discrepancy of a Lamé disc, an asymptotic formula is established for the number of lattice points in the three-dimensional body $$|u_1|^{mk}+\left(|u_2|^k+|u_3|^k\right)^{m}\le x^{mk},$$ for large real x and fixed reals m, k. Particular attention is paid to the boundary points of Gaussian curvature zero.     

Durable antibacterial Ag/polyacrylonitrile (Ag/PAN) hybrid nanofibers prepared by atmospheric plasma treatment and electrospinning

Durable antibacterial Ag/polyacrylonitrile (Ag/PAN) hybrid nanofibers were prepared by atmospheric plasma treatment and electrospinning. Atmospheric helium plasma treatment was first used to reduce the AgNO₃ precursor in pre-electrospinning solutions into metallic silver nanoparticles, followed by electrospinning into continuous and smooth nanofibers with Ag nanoparticles embedded in the matrix. SEM, TEM, and EDX spectra were used to study the structure and surface elemental composition of the nanofibers. Silver nanoparticles, with diameters ranging between 3 and 6 nm, were found to be uniformly dispersed in the nanofiber matrix. The Ag/PAN nanofibers exhibited slow and long-lasting silver ion release, which provided robust antibacterial activity against both Gram-positive Bacillus cereus and Gram-negative Escherichia coli microorganisms.     

Effects of dynamical couplings in IR spectra of the hydrogen bond in N-phenylacrylamide crystals

This article presents the investigation results of the polarized IR spectra of the hydrogen bond in N-phenylacrylamide crystals measured in the frequency range of the proton and deuteron, ν(N-H) and ν(N-D), stretching vibration bands. The basic spectral properties of the crystals were interpreted quantitatively in terms of the "strong-coupling" theory. The proposed model of the centrosymmetric dimer of hydrogen bonds facilitated the explanation of the well-developed, two-branch structure of the ν(N-H) and ν(N-D) bands as well as the isotopic dilution effects in the spectra. The vibronic mechanism of the generation of the long-wave branch of the ν(N-H) band ascribed to the excitation of the totally symmetric proton vibration was elucidated. The complex fine structure pattern of ν(N-H) and ν(N-D) bands in N-phenylacrylamide spectra in comparison with the spectra of other secondary amide crystals (e.g., N-methylacetamide and acetanilide) can be accounted for in terms of the vibronic model for the forbidden transition breaking in the dimers. On the basis of the linear dichroic and temperature effects in the polarized IR spectra of N-phenylacrylamide crystals, the H/D isotopic "self-organization" effects were revealed.     

Normal fields of functionals and optimal measurable sections

We study some classes of extended real-valued functions on measurable fields of metric spaces and give sufficient conditions for the existence of optimal measurable sections.The author is grateful to A. Kucia for Lemma 3.3, Theorem 3.1 (i), and helpful discussions.     

On the general asymmetric divisor problem

To ProfessorEkkehard Kr?tzel on his 60^th birthday     

Angular distribution of intensity of reflected radiation investigations of the influence of CO2 laser treatment on optical properties of hydrogenated amorphous silicon

Thin films of hydrogenated amorphous silicon (a-Si:H) were annealed using CO₂ laser radiation (λ=10.6 μm). Changes of optical properties of the treated a-Si:H were investigated using optical transmittance spectroscopy and the angular distribution of intensity of reflected radiation (ADIRR). The CO₂ laser annealing influences the spectral characteristics of the real part of refractive index n and absorption coefficient α of light in a-Si:H. This treatment increases the n and α values as well as the Urbach energy of a-Si:H. Simultaneously it decreases the optical energy gap of this material. The changes of optical parameters at the interfaces of a-Si:H–glass substrate and a-Si:H–air were established.     

Traffic noise reduction due to the porous road surface

Porous road surfaces reduce road traffic noise. A new method of noise reduction assessment is proposed. The noise generated by a few vehicles was measured two times: on an old surface with the dense asphalt and on a new surface with the porous asphalt. Subjective assessments of drive-by noise suggest that the sound exposure and the road surface coefficient can be used as the acoustical characteristics of a road surface. Their average values, with the average number of vehicles passing the receiver during a day or night, makes it possible to predict the equivalent continuous A-weighted sound pressure level for the new road surface. This is the main objective of this paper.     

Magnetic hysteresis in Ni/Pb multilayers

The hysteresis in Ni/Pb multilayers with layer thickness of 1.7, 5.5, 9.4 and 24.8 nm have been examined at low and room temperatures. The Stoner-Wohlfarth model, modified by the introduction of a constant internal field, well describes the shape of experimental hysteresis loops. The two components of internal field and anisotropy constant are fit to an individual loop. The transversal component of the internal field is related to a dispersion of local magnetization directions and determines a deviation of the rotation process from the Stoner-Wohlfarth model. At room temperature, the transversal component of the internal field for Ni/Pb multilayers is about 1000 Oe and is much greater than the effective anisotropy field and, as a result, the directions of magnetization rotate smoothly under the influence of resultant field. At low temperature, the longitudal component of the internal field is of the order of 1000 Oe and determines the incoherent rotations.     

The temperature-dependent absorption spectrum of the v3 band of SF6 at 10·6 μm

Mixtures of SF₆ diluted by argon were heated behind an incident shock front in the range 400 to 1500K. Absorption measurements at 11 wavelengths near 10·6 μm were made on the post-shock, equilibrated gas using a CO₂ laser. A band contour model, which makes use of known spectroscopic constantd and the experimental results, satisfactorily accounts for the observed temperature dependence of the absorption coefficient. We are able to estimate the identity of the transitions responsible for absorption of the laser radiation.