The Cole-Cole Law for Critical Dynamics in Glass-Forming Liquids

Within the mode-coupling theory (MCT) for glassy dynamics, the asymptotic low-frequency expansions for the dynamical susceptibilities at critical points are compared to the expansions for the dynamic moduli; this shows that the convergence properties of the two expansions can be quite different. In some parameter regions, the leading-order expansion formula for the modulus describes the solutions of the MCT equations of motion outside the transient regime successfully; at the same time, the leading- and next-to-leading order expansion formulas for the susceptibility fail. In these cases, one can derive a Cole-Cole law for the susceptibilities; and this law accounts for the dynamics for frequencies below the band of microscopic excitations and above the high-frequency part of the alpha-peak. It is shown that this scenario explains the optical-Kerr-effect data measured for salol and benzophenone (BZP). For BZP it is inferred that the depolarized light-scattering spectra exhibit a wing for the alpha-peak within the Gigahertz band. This wing results from the crossover of the von Schweidler-law part of the alpha-peak to the high-frequency part of the Cole-Cole peak; and this crossover can be described quantitatively by the leading-order formulas of MCT for the modulus.Comment: 15 pages, 9 figure

Critical Decay at Higher-Order Glass-Transition Singularities

Within the mode-coupling theory for the evolution of structural relaxation in glass-forming systems, it is shown that the correlation functions for density fluctuations for states at A_3- and A_4-glass-transition singularities can be presented as an asymptotic series in increasing inverse powers of the logarithm of the time t: $\phi(t)-f\propto \sum_i g_i(x)$, where $g_n(x)=p_n(\ln x)/x^n$ with p_n denoting some polynomial and x=ln (t/t_0). The results are demonstrated for schematic models describing the system by solely one or two correlators and also for a colloid model with a square-well-interaction potential.Comment: 26 pages, 7 figures, Proceedings of "Structural Arrest Transitions in Colloidal Systems with Short-Range Attractions", Messina, Italy, December 2003 (submitted

Dynamics in Colloidal Liquids near a Crossing of Glass- and Gel-Transition Lines

Within the mode-coupling theory for ideal glass-transitions, the mean-squared displacement and the correlation function for density fluctuations are evaluated for a colloidal liquid of particles interacting with a square-well potential for states near the crossing of the line for transitions to a gel with the line for transitions to a glass. It is demonstrated how the dynamics is ruled by the interplay of the mechanisms of arrest due to hard-core repulsion and due to attraction-induced bond formation as well as by a nearby higher-order glass-transition singularity. Application of the universal relaxation laws for the slow dynamics near glass-transition singularities explains the qualitative features of the calculated time dependence of the mean-squared displacement, which are in accord with the findings obtained in molecular-dynamics simulation studies by Zaccarelli et. al [Phys. Rev. E 66, 041402 (2002)]. Correlation functions found by photon-correlation spectroscopy in a micellar system by Mallamace et. al [Phys. Rev. Lett. 84, 5431 2000)] can be interpreted qualitatively as a crossover from gel to glass dynamics.Comment: 13 pages, 12 figure

Numerical study of the glass-glass transition in short-ranged attractive colloids

We report extensive numerical simulations in the {\it glass} region for a simple model of short-ranged attractive colloids, the square well model. We investigate the behavior of the density autocorrelation function and of the static structure factor in the region of temperatures and packing fractions where a glass-glass transition is expected according to theoretical predictions. We strengthen our observations by studying both waiting time and history dependence of the numerical results. We provide evidence supporting the possibility that activated bond-breaking processes destabilize the attractive glass, preventing the full observation of a sharp glass-glass kinetic transition.Comment: 15 pages, 9 figures; Proceedings of "Structural Arrest Transitions in Colloidal Systems with Short-Range Attractions", Messina, Italy, December 2003 (submitted to J. Phys.: Condens. Matt.

An asteroseismic test of diffusion theory in white dwarfs

The helium-atmosphere (DB) white dwarfs are commonly thought to be the descendants of the hotter PG1159 stars, which initially have uniform He/C/O atmospheres. In this evolutionary scenario, diffusion builds a pure He surface layer which gradually thickens as the star cools. In the temperature range of the pulsating DB white dwarfs (T_eff ~ 25,000 K) this transformation is still taking place, allowing asteroseismic tests of the theory. We have obtained dual-site observations of the pulsating DB star CBS114, to complement existing observations of the slightly cooler star GD358. We recover the 7 independent pulsation modes that were previously known, and we discover 4 new ones to provide additional constraints on the models. We perform objective global fitting of our updated double-layered envelope models to both sets of observations, leading to determinations of the envelope masses and pure He surface layers that qualitatively agree with the expectations of diffusion theory. These results provide new asteroseismic evidence supporting one of the central assumptions of spectral evolution theory, linking the DB white dwarfs to PG1159 stars.Comment: 7 pages, 3 figures, 3 tables, accepted for publication in A&

A search for solar-like oscillations in K giants in the globular cluster M4

To expand the range in the colour-magnitude diagram where asteroseismology can be applied, we organized a photometry campaign to find evidence for solar-like oscillations in giant stars in the globular cluster M4. The aim was to detect the comb-like p-mode structure characteristic for solar-like oscillations in the amplitude spectra. The two dozen main target stars are in the region of the bump stars and have luminosities in the range 50-140 Lsun. We collected 6160 CCD frames and light curves for about 14000 stars were extracted. We obtain high quality light curves for the K giants, but no clear oscillation signal is detected. High precision differential photometry is possible even in very crowded regions like the core of M4. Solar-like oscillations are probably present in K giants, but the amplitudes are lower than classical scaling laws predict.Comment: 14 pages, 16 figures, accepted for publication in A&

Immundefekte bei chronischer Rhinosinusitis : eine bedeutende und oft unterschätzte Ursache

Background Chronic rhinosinusitis (CRS) is one of the most frequent chronic diseases. Among these patients the prevalence of immune defects is higher than in the healthy general population. Methods A selective review of the literature was carried out in PubMed and Medline covering the period between 2008 and 2019. Additionally, recent German publications in journals not listed in the abovementioned databases were analyzed. Results The diagnostic workflow with respect to the immunodeficiency consists of a detailed anamnesis and physical examination, laboratory tests and the antibody reaction to polysaccharide vaccines and antigens. Beside antibiotic treatment, vaccinations and immunoglobulin replacement are available. Notwithstanding the above, functional endoscopic surgery of the paranasal sinuses should be performed according to guideline recommendations. Conclusion Patients with CRS who do not sufficiently respond to conservative and surgical treatment should be checked for underlying immunodeficiencies

Magnetic spin excitations in Mn doped GaAs : A model study

We provide a quantitative theoretical model study of the dynamical magnetic properties of optimally annealed Ga$_{1-x}$Mn$_x$As. This model has already been shown to reproduce accurately the Curie temperatures for Ga$_{1-x}$Mn$_x$As. Here we show that the calculated spin stiffness are in excellent agreement with those which were obtained from ab-initio based studies. In addition, an overall good agreement is also found with available experimental data. We have also evaluated the magnon density of states and the typical density of states from which the "mobility edge", separating the extended from localized magnon states, was determined. The power of the model lies in its ability to be generalized for a broad class of diluted magnetic semiconductor materials, thus it bridges the gap between first principle calculations and model based studies.Comment: 5 pages, 5 figures, Text and some figures revised to match the accepted versio

Theory and simulation of gelation, arrest and yielding in attracting colloids

We present some recent theory and simulation results addressing the phenomena of colloidal gelation at both high and low volume fractions, in the presence of short-range attractive interactions. We discuss the ability of mode-coupling theory and its adaptations to address situations with strong heterogeneity in density and/or dynamics. We include a discussion of the effect of attractions on the shear-thinning and yield behaviour under flow.Comment: 17 pages, 6 figure

Higher order glass-transition singularities in colloidal systems with attractive interactions

The transition from a liquid to a glass in colloidal suspensions of particles interacting through a hard core plus an attractive square-well potential is studied within the mode-coupling-theory framework. When the width of the attractive potential is much shorter than the hard-core diameter, a reentrant behavior of the liquid-glass line, and a glass-glass-transition line are found in the temperature-density plane of the model. For small well-width values, the glass-glass-transition line terminates in a third order bifurcation point, i.e. in a A_3 (cusp) singularity. On increasing the square-well width, the glass-glass line disappears, giving rise to a fourth order A_4 (swallow-tail) singularity at a critical well width. Close to the A_3 and A_4 singularities the decay of the density correlators shows stretching of huge dynamical windows, in particular logarithmic time dependence.Comment: 19 pages, 12 figures, Phys. Rev. E, in prin