18,203 research outputs found
Non-equilibrium phonon dynamics in trapped ion systems
We propose a concrete experiment to probe the non-equilibrium local dynamics
of the one-dimensional Bose-Hubbard model using a trapped ion system consisting
of a linear chain of few Ba^+ ions prepared in a state of transverse motional
mode which corresponds to a fixed number of phonons per ion. These phonons are
well-known to be described by an effective Bose-Hubbard model. We propose a
protocol which leads to a sudden local sign reversal of the on-site interaction
strength of this Hubbard model at one of the sites and demonstrate that the
subsequent non-equilibrium dynamics of the model can be experimentally probed
by measuring the time-dependent phonon number in a specific motional state of
the Ba+ ions. We back our experimental proposal with exact numerical
calculation of the dynamics of a Bose-Hubbard model subsequent to a local
quench.Comment: The submission contains 5 pages and 4 figure
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Investigation of Shallow Sedimentary Structure of the Anchorage Basin, Alaska, Using Simulated Annealing Inversion of Site Response
This study deals with shallow sedimentary structure of the Anchorage basin in Alaska. For this purpose, inversion of site response [SR(f)] data in the frequency range 0.5-11.0 Hz from various sites of the basin has been performed using the simulated annealing method to compute subsurface layer thickness, shear-wave velocity (beta), density, and shear-wave quality factor. The one-dimensional (1D) models for the aforementioned parameters were obtained with preset bounds on the basis of available geological information such that the L-2 norm error between the observed and computed site response attained a global minimum. Next, the spatial distribution of the important parameter beta was obtained by interpolating values yielded by the 1D models. The results indicate the presence of three distinct velocity zones as the source of spatial variation of SR(f) in the Anchorage basin. In the uppermost part of the basin, the beta values of fine-grain Quaternary sediments mainly lie in the range of 180-500 m/sec with thickness varying from 15 to 50 m. This formation overlies relatively thick (80-200 m) coarse-grain Quaternary sediments with beta values in the range of 600-900 m/sec. These two Quaternary units are, in turn, overlain on Tertiary sediments with beta > 1000 m/sec located at depths of 100 and 250 m, respectively, in the central and western side along the Knik Arm parts of the basin. The important implication of the result is that the sources of spatial variation of SR(f) in the Anchorage basin for the frequency band 0.5-11 Hz, besides in the uppermost 30 m, are found to be deeper than this depth. Thus, use of commonly considered geological formations in the depth intervals from 0 to 30 m for the ground-motion interpretation will likely yield erroneous results in the Anchorage basin.GIEnvironment and Natural Resources InstituteSchool of Engineering of the University of Alaska, AnchorageGeological Science
Hox Genes Regulate Muscle Founder Cell Pattern Autonomously and Regulate Morphogenesis Through Motor Neurons
The differentiation of myoblasts to form functional muscle fibers is a consequence of interactions between the mesoderm and ectoderm. The authors examine the role of segment identity in directing these interactions by studying the role of Hox genes in patterning adult muscles in Drosophila. Using the `four-winged fly' to remove Ultrabithorax function in the developing adult, the authors alter the identity of the ectoderm of the third thoracic segment towards the second and show that this is sufficient to inductively alter most properties of the mesoderm—myoblast number, molecular diversity, and migration pattern—to that of the second thoracic segment. Not all aspects of myogenesis are determined by the segment identity of the ectoderm. The autonomous identity of the mesoderm is important for choosing muscle founder cells in the correct segmental pattern. The authors show this by removal of the function of Antennapedia, the Hox gene expressed in the mesoderm of the third thoracic segment. This results in the transformation of founder cells to a second-thoracic pattern. The authors also report a role for the nervous system in later aspects of muscle morphogenesis by specifically altering Ultrabithorax gene expression in motor neurons. Thus, ectoderm and mesoderm segment identities collaborate to direct muscle differentiation by affecting distinct aspects of the process
Universal Scaling Property of System Approaching Equilibrium
In this Letter we show that the diffusion kinetics of kinetic energy among
the atoms in non- equilibrium crystalline systems follows universal scaling
relation and obey Levy-walk properties. This scaling relation is found to be
valid for systems no matter how far they are driven out of equilibrium.Comment: 6 pages, 4 figure
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