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[en] We developed the pulse sequence TOMROP (T One by Multiple Read Out Pulses) for determining precisely the spatial distribution of the longitudinal relaxation time T1 in nuclear magnetic resonance (NMR): a series of small-angle selection pulses is used to read out longitudinal magnetization from its initial state till thermal equilibrium. Hence, one measurement will produce several images with different T1 weightings whose pixel brilliance depends exponentially from read-out time. T1 can be determined from these independent of initial magnetization and selection pulse angle. The measuring time corresponds to the time needed in multi-echo imaging for the determination of the transversal relaxation time T2. We demonstrate this new method using head images of volunteers produced with a 0.23 T test facility. (orig./HP)
[de]Zur genauen Bestimmung der raeumlichen Verteilung der Laengsrelaxation T1 in der Kernspintomographie haben wir die Pulssequenz-TOMROP (T One by Multiple Read Out Pulses) entwickelt: Mit einer Serie von Kleinwinkelauslesepulsen wird die Laengsmagnetisierung vom Anfangszustand bis zum thermischen Gleichgewicht abgefragt. In einer Messung ergeben sich also mehrere unterschiedlich T1-gewichtete Bilder, bei denen die Pixelhelligkeit exponentiell von der Abfragezeit abhaengt. Hieraus kann T1 unabhaengig von der Anfangsmagnetisierung und dem Auslesepulswinkel bestimmt werden. Die Messzeit entspricht der einer Multiechoaufnahme zur Bestimmung der Querrelaxationszeit T2. Mit einer 0,23-T-Versuchsanlage demonstrieren wir das neue Verfahren an Kopfaufnahmen von freiwilligen Versuchspersonen. (orig./HP)
[en] We study the entanglement dynamics and relaxation properties of a system of two interacting qubits in the cases of (I) two independent bosonic baths and (II) one common bath. We find that in the case (II) the existence of a decoherence-free subspace (DFS) makes entanglement dynamics very rich. We show that when the system is initially in a state with a component in the DFS the relaxation time is surprisingly long, showing the existence of semi-decoherence free subspaces.
[en] We review our recent proposal for a universal description of generic single-component viscoelastic systems with a single relaxation time. Foliation preserving diffeomorphisms are introduced as an underlying symmetry which naturally interpolates between the two extreme characters of elasticity and fluidity. The symmetry is found to be powerful enough to determine the dynamics in the first order of strains
[en] The dynamic critical exponent z is determined from numerical simulations for the three-dimensional (3D) lattice Coulomb gas (LCG) and the 3D XY models with relaxational dynamics. It is suggested that the dynamics is characterized by two distinct dynamic critical indices z0 and z related to the divergence of the relaxation time τ by τ∝ξz0 and τ∝k-z , where ξ is the correlation length and k the wave vector. The values determined are z0∼1.5 and z∼1 for the 3D LCG and z0∼1.5 and z∼2 for the 3D XY model. Comparisons with other results are discussed
[en] We present Expanded Very Large Array (EVLA) D-array observations of the 21 cm line of neutral hydrogen (H I) of CIG 292, an isolated SA(s)b galaxy at a distance of ∼24.3 Mpc. From previous H I single dish observations the galaxy was known to have a mildly asymmetric H I profile (A flux = 1.23 ± 0.3). Our EVLA observations show there is ∼12% more H I projected south of the optical center (approaching velocities) than in the north (receding velocities), despite the H I extending ∼16% further to the north than the south. The H I projected within the optical disk must have been perturbed within the H I relaxation time (∼108 yr) which implies that this cannot have been caused by any of the three nearest companions, as their distance (∼0.5 Mpc) is too large. Neither H I-rich companions nor tidal tails were found within our field of view and velocity range covered. Our kinematical data suggest that the inner part harbors an oval distortion whereas the outer regions show signs of a modest warp. The mild asymmetry in the H I global profile thus actually masks stronger asymmetries in the two-dimensional distributions of gas and star-forming regions in this galaxy. Since the galaxy is isolated, this must predominantly be due to processes related to its formation and secular evolution.
[en] The theoretical problems related to the Brochard-Leger wall in liquid crystals have been further explicated. It has been shown that there exists a critical region in liquid crystals, beyond which the Brochard-Leger wall does not exist. The relaxation behaviour of the wall has been discussed, and the relaxation time has been calculated. The speed of the Brochard-Leger wall has been investigated for the case for which the tilt angle of the external field is equal to a critical angle. (author)
[en] We investigate the influence of space curvature, and of the associated frustration, on the dynamics of a model glass former: a monatomic liquid on the hyperbolic plane. We find that the system's fragility, i.e., the sensitivity of the relaxation time to temperature changes, increases as one decreases the frustration. As a result, curving space provides a way to tune fragility and make it as large as wanted. We also show that the nature of the emerging 'dynamic heterogeneities', another distinctive feature of slowly relaxing systems, is directly connected to the presence of frustration-induced topological defects
[en] Although fragility of glass forming liquids is traditionally related to cooperativity in molecular motion, the connection between those parameters remains unclear. In this paper we present the estimates of cooperativity (heterogeneity) length scale obtained from the boson peak spectra. We demonstrate that agrees well with the dynamic heterogeneity length scale for the structural relaxation estimated by 4- dimensional NMR, justifying the use of . Presented analysis of large number of materials reveals no clear correlation between and fragility. However, there is a strong correlation between the cooperativity volume 3 and the activation volume measured at Tg. This observation suggests that only the volume (pressure) dependence of structural relaxation time correlates directly with the cooperativity size. However, the pure thermal (energetic) contribution to the structural relaxation, the so-called isochoric fragility, exhibits no correlation to the heterogeneity length scale, or the amount of structural units in 3. The presented results call for a revision of traditional view on the role of cooperativity/heterogeneity in structural relaxation of glass forming systems.