Zur Theorie des Schwingungs-EIastoviskosimeters

Zusammenfassung Die elastoviskosen Eigenschaften von Flüssigkeiten und Gelen werden bekanntlich unter anderem-mit Hilfe von Schwingungs-Elastoviskosimetern untersucht. Ein derartiger Test spiegelt nicht unmittelbar die interessierenden Eigenschaften der Prüfsubstanz, sondern das mechanische Verhalten des aus der Prüfsubstanz und der Meßapparatur bestehenden Simultansystems wider, welches durch die Massenträgheit der Apparatur und der Prüfsubstanz beeinflußt wird.Dieses mechanische Verhalten des Systems wird in der Arbeit theoretisch eingehend untersucht (das ebene Problem), und die exakten Auswertungsformeln zur Bestimmung der elastoviskosen Eigenschaften der getesteten Substanzen werden entwickelt. Ferner wird der Resonanztest diskutiert und, fußend auf einer Approximation durch eine äquivalenteMaxwell-Substanz, ein Fluchtlinien-Nomogramm zur Berechnung des Verlustwinkels im Resonanzpunkt angegeben. Die aufgestellten theoretischen Beziehungen wurden zur Auswertung einiger experimenteller Ergebnisse in einem Frequenzbereich von 10–10³ Hz herangezogen.Zum 100jährigen Jubiläum der Farbenfabriken Bayer A. G. Vorgetragen auf der Rheologentagung, Bad Oeynhausen, März 1963.     

The thermotropic and lyotropic liquid-crystalline properties of acetoacetoxypropyl cellulose

Acetoacetoxypropyl cellulose, formed by the acetoacetylation of hydroxypropyl cellulose using a diketene/acetone adduct at elevated temperature, forms both thermotropic and lyotropic liquid-crystalline phases. DSC and hot-stage polarized light microscopy confirmed the thermotropic nature of the bulk polymer. Thin layers showed green reflection colors at room temperature. The wavelength λ₀ of selective reflection was measured spectrophotometrically. The crystalline structure of the polymer was investigated using x-ray diffraction. A lyotropic mesophase formed in acetic acid at ≥ 40 wt% polymer. The value of λ₀ for the lyotropic cholesteric mesophase was determined by optical rotatory dispersion (ORD) and circular dichroism (CD) of a thin layer of a wholly anisotropic solution.     

Asymptotic freedom of Yang–Mills theory with gravity

We study the behaviour of Yang–Mills theory under the inclusion of gravity. In the weak-gravity limit, the running gauge coupling receives no contribution from the gravitational sector, if all symmetries are preserved. This holds true with and without cosmological constant. We also show that asymptotic freedom persists in general field-theory-based gravity scenarios including gravitational shielding as well as asymptotically safe gravity.     

Quantum nature of the big bang

Some long-standing issues concerning the quantum nature of the big bang are resolved in the context of homogeneous isotropic models with a scalar field. Specifically, the known results on the resolution of the big-bang singularity in loop quantum cosmology are significantly extended as follows: (i) the scalar field is shown to serve as an internal clock, thereby providing a detailed realization of the "emergent time" idea; (ii) the physical Hilbert space, Dirac observables, and semiclassical states are constructed rigorously; (iii) the Hamiltonian constraint is solved numerically to show that the big bang is replaced by a big bounce. Thanks to the nonperturbative, background independent methods, unlike in other approaches the quantum evolution is deterministic across the deep Planck regime.     

Far-from-equilibrium quantum many-body dynamics

A theory of real-time quantum many-body dynamics is evaluated in detail. It is based on a generating functional of correlation functions where the closed time contour extends only to a given time. Expanding the contour from this time to a later time leads to a dynamic flow of the generating functional. This flow describes the dynamics of the system and has an explicit causal structure. In the present work it is evaluated within a vertex expansion of the effective action leading to time-evolution equations for Green functions. These equations are applicable for strongly interacting systems as well as for studying the late-time behavior of non-equilibrium time evolution. For the specific case of a bosonic $\mathcal{N}$ -component φ ⁴-theory with contact interactions an s-channel truncation is identified to yield equations identical to those derived from the 2PI effective action in next-to-leading order of a $1/\mathcal{N}$ expansion. The presented approach allows to directly obtain non-perturbative dynamic equations beyond the widely used 2PI approximations.     

Studies on the valence electronic structure of Fe and Ni in Fe x Ni1−x alloys

K _β-to-K _α X-ray intensity ratios of Fe and Ni in pure metals and in Fe _x Ni_1−x alloys (x=0.20, 0.50, 0.58) exhibiting similar crystalline structure have been measured following excitation by 59.54 keV γ-rays from a ²⁴¹Am point source, to understand as to why the properties of permalloy Fe_0.2Ni_0.8 is distinct from other alloy compositions. It is observed that the valence electronic structure of Fe_0.2Ni_0.8 alloy is totally different from other alloys which may be attributed to its special magnetic properties.