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Search Results: 1 - 10 of 189872 matches for " G. Gruebel "
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Investigating liquid surfaces down to the nanometer scale using grazing incidence x-ray scattering
C. Fradin,A. Braslau,D. Luzet,M. Alba,C. Gourier,J. Daillant,G. Gruebel,G. Vignaud,J. -F. Legrand,J. Lal J. -M. Petit,F. Rieutord
Physics , 1997, DOI: 10.1016/S0921-4526(98)00255-5
Abstract: Grazing incidence x-ray surface scattering has been used to investigate liquid surfaces down to the molecular scale. The free surface of water is well described by the capillary wave model ( ~ q-2 spectrum) up to wavevectors > 10^8 m^-1. At larger wavevectors near-surface acoustic waves must be taken into account. When the interface is bounded by a surfactant monolayer, it exhibits a bending stiffness and the bending rigidity modulus can be measured. However, bending effects generally cannot be described using the Helfrich Hamiltonian and the characteristic exponent in the roughness power spectrum can smaller than 4. Finally, upon compression, tethered monolayers formed on a subphase containing divalent ions are shown to buckle in the third dimension with a characteristic wavelength on the order of 10^8 m^-1.
Trickle-down processes and their boundaries
Steven N. Evans,Rudolf Gruebel,Anton Wakolbinger
Mathematics , 2010,
Abstract: It is possible to represent each of a number of Markov chains as an evolving sequence of connected subsets of a directed acyclic graph that grow in the following way: initially, all vertices of the graph are unoccupied, particles are fed in one-by-one at a distinguished source vertex, successive particles proceed along directed edges according to an appropriate stochastic mechanism, and each particle comes to rest once it encounters an unoccupied vertex. Examples include the binary and digital search tree processes, the random recursive tree process and generalizations of it arising from nested instances of Pitman's two-parameter Chinese restaurant process, tree-growth models associated with Mallows' phi model of random permutations and with Schuetzenberger's non-commutative q-binomial theorem, and a construction due to Luczak and Winkler that grows uniform random binary trees in a Markovian manner. We introduce a framework that encompasses such Markov chains, and we characterize their asymptotic behavior by analyzing in detail their Doob-Martin compactifications, Poisson boundaries and tail sigma-fields.
Supplemental Material for "High Contrast X-ray Speckle from Atomic-Scale Order in Liquids and Glasses"
S. O. Hruszkewycz,M. Sutton,P. H. Fuoss,B. Adams,S. Rosenkranz,K. F. Ludwig Jr.,W. Roseker,D. Fritz,M. Cammarata,D. Zhu,S. Lee,H. Lemke,C. Gutt,A. Robert,G. Gruebel,G. B. Stephenson
Physics , 2012,
Abstract: This supplemental material gives additional detail on Experimental Methods and Hard X-ray FEL Source Characteristics, Calculation of Maximum Speckle Contrast, Extracting Contrast of Weak Speckle Patterns, Estimated Temperature Increase from X-ray Absorption, Split-Pulse XPCS Feasibility, and Sample Disturbance During Single Pulses.
High Contrast X-ray Speckle from Atomic-Scale Order in Liquids and Glasses
S. O. Hruszkewycz,M. Sutton,P. H. Fuoss,B. Adams,S. Rosenkranz,K. F. Ludwig Jr.,W. Roseker,D. Fritz,M. Cammarata,D. Zhu,S. Lee,H. Lemke,C. Gutt,A. Robert,G. Gruebel,G. B. Stephenson
Physics , 2012, DOI: 10.1103/PhysRevLett.109.185502
Abstract: The availability of ultrafast pulses of coherent hard x-rays from the Linac Coherent Light Source opens new opportunities for studies of atomic-scale dynamics in amorphous materials. Here we show that single ultrafast coherent x-ray pulses can be used to observe the speckle contrast in the high-angle diffraction from liquid Ga and glassy Ni2Pd2P and B2O3. We determine the thresholds above which the x-ray pulses disturb the atomic arrangements. Furthermore, high contrast speckle is observed in scattering patterns from the glasses integrated over many pulses, demonstrating that the source and optics are sufficiently stable for x-ray photon correlation spectroscopy studies of dynamics over a wide range of time scales.
Ultrafast Laser-Induced Melting of Long-Range Magnetic Order in Multiferroic TbMnO3
Jeremy A. Johnson,T. Kubacka,M. C. Hoffmann,C. Vicario,S. de Jong,P. Beaud,S. Gruebel,S. -W. Huang,L. Huber,Y. W. Windsor,E. M. Bothschafter,L. Rettig,M. Ramakrishnan,A. Alberca,L. Patthey,Y. -D. Chuang,J. J. Turner,G. L. Dakovski,W. -S. Lee,M. P. Minitti,W. Schlotter,R. G. Moore,C. P. Hauri,S. M. Koohpayeh,V. Scagnoli,G. Ingold,S. L. Johnson,U. Staub
Physics , 2015,
Abstract: We performed ultrafast time-resolved near-infrared pump, resonant soft X-ray diffraction probe measurements to investigate the coupling between the photoexcited electronic system and the spin cycloid magnetic order in multiferroic TbMnO3 at low temperatures. We observe melting of the long range antiferromagnetic order at low excitation fluences with a decay time constant of 22.3 +- 1.1 ps, which is much slower than the ~1 ps melting times previously observed in other systems. To explain the data we propose a simple model of the melting process where the pump laser pulse directly excites the electronic system, which then leads to an increase in the effective temperature of the spin system via a slower relaxation mechanism. Despite this apparent increase in the effective spin temperature, we do not observe changes in the wavevector q of the antiferromagnetic spin order that would typically correlate with an increase in temperature under equilibrium conditions. We suggest that this behavior results from the extremely low magnon group velocity that hinders a change in the spin-spiral wavevector on these time scales.
Toward a single mode Free Electron Laser for coherent hard x-ray experiments
Sooheyong Lee,Zhirong Huang,Yuantao Ding,Paul Emma,Wojciech Roseker,Gerhard Gruebel,Aymeric Robert
Physics , 2010,
Abstract: The fluctuations of the longitudinal coherence length expected from the world's first hard X-ray Free Electron Laser, the Linac Coherent Light Source, are investigated. We analyze, on a shot-to-shot basis, series of power spectra generated from 1D-FEL simulations. We evaluate how the intrinsic noise in the spectral profile of the X-ray beam reflects on its longitudinal coherence length. We show that the spectral stability of the LCLS beam will allow coherent X-ray experiments with a reasonable acquisition time. We also propose a scheme to deliver single-mode X-ray radiation using a narrow bandpass monochromator.
A Characterization of the Members of a Subfamily of Power Series Distributions  [PDF]
G. Nanjundan
Applied Mathematics (AM) , 2011, DOI: 10.4236/am.2011.26099
Abstract: This paper discusses a characterization of the members of a subfamily of power series distributions when their probability generating functions satisfy the functional equation where a, b and c are constants and is the derivative of f.
Double Negative Left-Handed Metamaterials for Miniaturization of Rectangular Microstrip Antenna  [PDF]
G. Singh
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2010, DOI: 10.4236/jemaa.2010.26044
Abstract: In this paper, I have explored a significant concept for the miniaturization of microstrip patch antenna configuration by using the double negative (DNG) left-handed Metamaterials, which have dielectric permittivity and magnetic permeability both negative, simultaneously. It is achieved through the concept of phase-compensation by thin slab consist of the double positive (DPS) material, which have dielectric permittivity and magnetic permeability both positive, simultaneously and DNG metamaterials as a substrate of the microstrip patch antenna. By combining the DNG metamaterial slab with the slab made of DPS materials form a cavity resonator whose dispersion relation is independent of the sum of thickness of the slabs filling this cavity but it depends on the ratio of their thicknesses. This cavity constitutes by DPS and DNG material is used as substrate of the microstrip antennas and the DNG material slab is behave as phase compensator.
Dynamic and Configurational Approach to the Glass Transition by Nanoscale Cooperativity  [PDF]
G. Romeo
Open Journal of Biophysics (OJBIPHY) , 2012, DOI: 10.4236/ojbiphy.2012.23012
Abstract: Here we examine the findings obtained for disaccharide/water mixtures near glass transition that involves cooperative relaxation features on kinetic by viscosity and on thermodynamic behaviour by neutron scattering. Then to address cooperative phenomena that mitigate the Debye-Waller behaviour we invoke Adam-Gibbs’ idea of a cooperative rearranging region. Neutron results suggest that the excess mean square displacement behaves as free volume and is closely connected to an elementary step of the structural relaxation. Then viscosity data evidence a breakdown of the Einstein-Debye relation, decoupling attributed to the intermolecular cooperativity.
Confidence Level Estimator of Cosmological Parameters  [PDF]
G. Sironi
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.329157
Abstract: Cosmological Models frequently suggest the existence of physical, quantities, e.g. dark energy, we cannot yet observe and measure directly. Their values are obtained indirectly setting them equal to values and accuracy of the associated model parameters which best fit model and observation. Apparently results are so accurate that some researchers speak of precision cosmology. The accuracy attributed to these indirect values of the physical quantities however does not include the uncertainty of the model used to get them. We suggest a Confidence Level Estimator to be attached to these indirect measurements and apply it to current cosmological models.
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