Time-dependent optical linewidth in fluctuating environments: Stochastic models

Time-resolved optical lineshapes are calculated using a second-order inhomogeneous cumulant expansion. The calculation shows that in the inhomogeneous limit the optical spectra are determined solely by two-time correlation functions. Therefore, measurements of the Stokes-shift correlation function and the inhomogeneous linewidth cannot provide information about the heterogeneity lifetime for systems exhibiting dynamic heterogeneities. The theoretical results are illustrated using a stochastic model for the optical transition frequencies. The model rests on the assumption that the transition frequencies are coupled to the environmental relaxation of the system. The latter is chosen according to a free-energy landscape model for dynamically heterogeneous dynamics. The model calculations show that the available experimental data are fully compatible with a heterogeneity lifetime on the order of the primary relaxation time.Comment: 19 pages, 4 figure

Aging in a free-energy landscape model for glassy relaxation

The aging properties of a simple free-energy landscape model for the primary relaxation in supercooled liquids are investigated. The intermediate scattering function and the rotational correlation functions are calculated for the generic situation of a quench from a high temperature to below the glass transition temperature. It is found that the re-equilibration of molecular orientations takes longer than for translational degrees of freedom. The time scale for re-equilibration is determined by that of the primary relaxation as an intrinsic property of the model.Comment: 17 pages, 10 figure

Nonresonant holeburning in the Terahertz range: Brownian oscillator model

The response to the field sequence of nonresonant hole burning, a pump-wait-probe experiment originally designed to investigate slow relaxation in complex systems, is calculated for a model of Brownian oscillators, thus including inertial effects. In the overdamped regime the model predictions are very similar to those of the purely dissipative stochastic models investigated earlier, including the possibility to discriminate between dynamic homogeneous and heterogeneous relaxation. The case of underdamped oscillations is of particular interest when low-frequency excitations in glassy systems are considered. We show that also in this situation a frequency selective modification of the response should be feasable. This means that it is possible to specifically address various parts of the spectrum. An experimental realization of nonresonant holeburning in the Terahertz regime therefore is expected to shed further light on the nature of the vibrations around the so-called boson peak.Comment: 23 pages, 6 figure

Disadvantaged youth between obedience and autonomy : a study of social deprivation

Der Diskurs über Benachteiligte offenbart einen Widerspruch zwischen formalen Normen und ihrer materialen Realisierung. Einerseits ist - dem ethisch-demokratischen Postulat von Zivilgesellschaft folgend - über die Codierungen des Sozialgesetzbuchs gesellschaftliche Teilnahme intendiert; es besteht also ein gesellschaftliches Versprechen auf gelingende Subjektkonstitution über den Ausbildungs- und Arbeitsmarkt. Andererseits gelingt der nationalen Bildungsberichterstattung zu Folge jährlich einem erheblichen Teil der Kohorte an Schulabgängern die Aufnahme eines Aus- bzw. Arbeitsverhältnisses nicht, und es fehlt gleichzeitig an gesellschaftlich adäquaten Institutionen, um das Versprechen auf Teilhabe faktisch werden zu lassen. Umso befremdlicher wirken verstärkt auftretende Klagen über (zukünftig) fehlende Facharbeiterbedarfe. Geht man davon aus, dass die Klärung der Subjektkonstitution der zentrale Gegenstandsbereich der Bildungsforschung ist, dann zeigt sich im Diskurs über Benachteiligte zwar noch eine marginale Beschäftigung mit Fragen der Subjektkonstitution. Der Zusammenhang von gesellschaftlichen Widerspruchslagen und Subjektkonstitution gehört indes nicht mehr zum Gegenstand erziehungswissenschaftlicher Untersuchungen, wenn es um benachteiligte Jugendliche geht. Demgegenüber herrschen eher Erklärungsversuche vor, welche die Subjektkonstitution auf Migrationshintergründe, sozio-kulturelle Herkunft oder Schulerfolg beschränken. Für die Planung, Steuerung und Regulation von Bildungsprozessen reicht das so generierte Wissen allerdings nicht aus, weil es die Ebenen der Vermittlung des Subjektes mit der Welt, also die Produktions- und Reproduktionsverhältnisse von Individuum und Gesellschaft nicht erhellt und somit nicht zur Klärung von Fragen der Subjektkonstitution beitragen kann. Gegenstand der wissenschaftlichen Untersuchung im Rahmen der vorliegenden Arbeit ist deshalb der Versuch, von der regulativen Leitidee der Konfiguration bzw. Kopplung der Prozesse von Sozio- und Psychogenese (vgl. Elias) ausgehend danach zu fragen, wie gesellschaftliche Bestimmungen und Sozialcharaktere die Subjektkonstitution beeinflussen.The scientific discourse about disadvantaged youth reveals a contradiction between formal norms and their realization. On the one hand, the judicial codification within the German Code of Social Law - following the democratic-ethical posit of civil society –aims for social inclusion which must be interpreted as a social promise of successful constitution of the human subject via the market of vocational training and the employment market itself. On the other hand, annual reports on the state of education in Germany reveal that there is a significant number of graduates who are excluded from the market of vocational training. At the same time there is a lack of adequate institutions, which consequently prevents/inhibits the realization of social inclusion of the aforementioned. A fortiori claims about the (potentially) uncovered demand of skilled workers in the future must surprise. Acting on the assumption that elucidation of the constitution of the human subject is the core universe of discourse in educational research, the scientific discourse on disadvantaged youth only marginally deals with the constitution of the human subject. The relation between social contradictions, the implicit social orders to cope and the constitution of the human subject however are not subject to educational science in the context of research on disadvantaged youth. In contrast, social exclusion of disadvantaged youth is attempted to be explained by monocausally having recourse on migration background, socio-cultural heritage or success in school. The knowledge that is being generated in this way is insufficient concerning processes of educational planning and regulation because it does not help to elucidate the levels of intermediation between the human subject and the world, namely the relations of production and reproduction of person and society and thus it does not contribute to elucidate questions of subject constitution. Therefore the object of this scientific investigation of this study - emanating from Elias' concept about the interconnection of sociogenesis and psychogenesis - to elucidate the impact of social dispositions and rationalities and social characters on the constitution of the human subject

Aging effects in simple models for glassy relaxation

Aging effects in the two-time correlation function and the response function after a quench from a high temperature to some low temperature are considered for a simple kinetic random energy model exhibiting stretched exponential relaxation. Because the system reaches thermal equilibrium for long times after the quench, all aging effect are of a transient nature. In particular, the violations of the fluctuation-dissipation theorem are considered and it is found that the relation between the response and the two-time correlation function depends on another function, the so-called asymmetry. This asymmetry vanishes in equilibrium but cannot be neglected in the aging regime. It is found that plots of the integrated response versus the correlation function are not applicable to quantify the violations of the fluctuation-dissipation theorem in this particular model. This fact has its origin in the absence of a scaling form of the correlation.Comment: revised versio