High-elasticity of polyisobutylene and polystyrene solutions

Summary A study is made of the high-elastic properties of solutions of polyisobutylene and polystyrene in a range of solvents of different quality with respect to these polymers. Measurements were carried out at room temperature in the concentration range 20–100% for polyisobutylene and 20–67% for polystyrene.It is shown that in contrast to the known effect of the nature of solvent on the viscous properties of polystyrene, the modulus of high elasticity of polystyrene solutions, as well as those of the flexible-chain polymer (polyisobutylene), measured in the linear range of mechanical behaviour of the system, depends only on the content of polymer in the solution and is practically independent of the nature of solvent.In the region of fairly high molecular weights the modulus of high elasticity is independent of the molecular weight of monodisperse polymers, but decreases with broadening MWD. The predominating role is not that of the high-molecular-weight fractions, but of the width of MWD.At high shear rates in the case of solutions of polymers in good solvents the variations of the modulus with shear rate is of an external nature, so that with shear rate is of an external nature, so that with a very high viscosity anomaly the modulus can decrease.

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Zusammenfassung Es werden die hochelastischen Eigenschaften von Polyisobutylen-bzw. Polystyrol-Lösungen untersucht, wobei verschiedene Lösungsmittel eingesetzt werden. Die Messungen wurden bei Raumtemperatur im Konzentrationsbereich von 20–100% bei Polyisobutylen und von 20–67% bei Polystyrol durchgeführt.Es zeigt sich, daß sowohl der Hochelastizitätsmodul von Styrol-Lösungen als auch der Modul von Polyisobutylen im linearen mechanischen Bereich nur vom polymeren Gehalt der Lösung und nicht vom Lösungsmittel abhängt. Dieses Verhalten weicht von den Viskositätseigenschaften ab, die bekanntlich durch das Lösungsmittel mitbestimmt werden.Im Bereich recht hoher Molekulargewichte wird der Modul der Hochelastizität unabhängig vom Molekulargewicht monodisperser Systeme, hingegen sinkt er mit breiter werdender Molekulargewichtsverteilung ab. Die beherrschende Rolle spielt nicht der Antcil des hohen Molekulargewichts, sondern die Molekulargewichtsverteilung.Bei hohen Schergeschwindigkeiten ist in guten Lösungsmitteln die Modulabhängigkeit von dieser Geschwindigkeit durch äußere Umstände bedingt, so daß bei sehr großer Viskositätsanomalie der Modul sinken kann.

     

Zur Stabilitätsfrage Rotierender Elastischer Stäbe

Ohne ZusammenfassungDie nachstehende Arbeit bildet eine namentlich nach der variationstheoretischen Seite hin orientierte Weiterentwickelung einer von der philosophischen Fakultät der Friedrich-Wilhelm-Universität Berlin genehmigten Doktor-Dissertation (Referenten: Prof. Dr. R. v. Mises, Geheimrat Prof. Dr. M. Planck.)     

Temperature-frequency reduction of the dynamic functions of black-filled rubbers in the nonlinear region

The possibility of using temperature-frequency reduction of the dynamic functions of black-filled rubbers in the nonlinear region is demonstrated and an additional applicability criterion — similar slopes of the isotherms of the amplitude dependences of the dynamic functions — is formulated. In the case of heavily filled rubbers it may be necessary to determine the constants of the Williams-Landel-Ferry equation and the reference temperature T_S from the experimental data — they may not coincide with the universal values. Master curves of the dynamic functions are obtained for a series of shock-absorbing rubbers at a shear strain amplitude =0.01.A. V. Topchiev Institute of Petrochemical Synthesis, Academy of Sciences of the USSR, Moscow. Scientific-Research Institute of the Rubber Industry, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 751–754, July–August, 1973.     

Quasi-optical theory of amplification of surface waves propagating above corrugated structures by a relativistic electron beam (impedance approximation)

The impedance model that describes the amplification of a monochromatic wave by a relativistic electron beam that propagates rectilinearly over a corrugated structure is constructed based on quasi-optical approach. In this model, the electric field component acting on electrons is written taking into account induced rf fields of the space charge of the beam. The dispersion equation used to determine the instability increments in various ranges of parameters has been obtained in the weak signal approximation. The efficiency of the energy exchange at the saturation stage of amplification is determined using a 2D nonlinear model in which the propagation of the wave has been described by a parabolic equation with a radiative boundary condition. The possibility of using the system under investigation to amplify submillimeter radiation has been demonstrated.     

Key plasma parameters for resonant backward Raman amplification in plasma

Backward Raman amplification and compression in plasma enables pulse compression to intensities not available using material gratings. In order to achieve the highest intensities and efficiencies in the compression effect, in a manner robust both to noise and other competing plasma effects, both resonance effects and detuning effects are exploited. Here we offer a simplified guide to how some of the key plasma parameters and laser parameters should be picked in order to achieve robust and efficient amplification.     

Quasi-optical theory of coaxial and cylindrical relativistic surface-wave oscillators

In terms of a quasi-optical approach, a nonlinear nonstationary theory of surface-wave oscillators, coaxial and cylindrical multiwave Cherenkov oscillators (MCOs) fed by large-diameter tubular electron beams, is constructed. The small curvature of the waveguide walls allows one to appreciably simplify the MCO dynamics analysis by considering a quasi-plane model. In this model, local surface fields near the corrugated cylindrical wall are close to fields of a plane corrugated with the same depth and period and the cylindrical geometry is taken into account by introducing azimuthal periodicity conditions. The results obtained in terms of the averaged approach are compared with those of direct numerical particle-in-cell (PIC) simulation and experimental data. Remarkably, PIC simulation demonstrates the existence of a single-frequency oscillation regime at long perimeters in which the self-synchronization of different azimuthal modes takes place. As a result, an azimuthally asymmetric stationary field distribution sets in, which can be assigned to dissipative structures well known in the theory of self-sustained oscillation systems.     

Superhyperfine structure of the EPR spectra of Ce<Superscript>3+</Superscript> ions in Li<Emphasis Type="Italic">R</Emphasis>F<Subscript>4</Subscript> (<Emphasis Type="Italic">R</Emphasis> = Y,Lu, Tm) double fluorides

The EPR spectra of Ce³⁺ impurity ions in LiYF₄, LiLuF₄, and LiTmF₄ double-fluoride single crystals have been investigated at a frequency of ∼9.3 GHz in the temperature range 5–25 K. The effective g factors of the ground Kramers doublet of the cerium ions in three crystals are close to each other (g _‖ = 2.737, g _⊥ = 1.475 for LiYF₄:Ce³⁺). A superhyperfine structure of the EPR spectrum of Ce³⁺ ions in the LiTmF₄ Van Vleck paramagnet has been observed in the external magnetic field B oriented along the crystallographic axis c (B ‖ c). The superhyperfine structure of the EPR soectra of the Ce³⁺ ions in the LiYF₄ and LiLuF₄ diamagnetic matrices is resolved for B ⊥ c. Possible factors responsible for this pronounced difference in the properties of the systems studied have been discussed.     

Short-wave sectioned free-electron masers with Bragg resonators based on the traveling and quasi-critical wave coupling

We consider the possibility of implementation of a free-electron maser with a two-mirror resonator composed of modified and conventional Bragg mirrors, operated in the short-wave part of the millimeter-wave range. The use of a modified Bragg mirror based on the traveling and quasicritical wave coupling at the input of the interaction space permits the transverse-index selection of modes. Amplification of the synchronous co-propagating wave by an electron beam is reached mainly in the regular part of the resonator. Even slight reflections from the conventional output Bragg cavity, which directly couples the co- and counter-propagating traveling waves, turn out to be sufficient for generation of self-excited oscillations. It is shown that the new scheme of a free electron maser ensures the oscillation frequency stabilization with respect to the electron-energy variation. With the optimal choice of the parameters, the oscillation frequency is close to the cutoff frequency of a quasi-critical wave excited in the modified Bragg structure.