1,127 research outputs found

    Electrophoretic Properties of Highly Charged Colloids: A Hybrid MD/LB Simulation Study

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    Using computer simulations, the electrophoretic motion of a positively charged colloid (macroion) in an electrolyte solution is studied in the framework of the primitive model. Hydrodynamic interactions are fully taken into account by applying a hybrid simulation scheme, where the charged ions (i.e. macroion and electrolyte), propagated via molecular dynamics (MD), are coupled to a Lattice Boltzmann (LB) fluid. In a recent experiment it was shown that, for multivalent salt ions, the mobility μ\mu initially increases with charge density σ\sigma, reaches a maximum and then decreases with further increase of σ\sigma. The aim of the present work is to elucidate the behaviour of μ\mu at high values of σ\sigma. Even for the case of monovalent microions, we find a decrease of μ\mu with σ\sigma. A dynamic Stern layer is defined that includes all the counterions that move with the macroion while subject to an external electrical field. The number of counterions in the Stern layer, q0q_0, is a crucial parameter for the behavior of μ\mu at high values of σ\sigma. In this case, the mobility μ\mu depends primarily on the ratio q0/Qq_0/Q (with QQ the valency of the macroion). The previous contention that the increase in the distortion of the electric double layer (EDL) with increasing σ\sigma leads to the lowering of μ\mu does not hold for high σ\sigma. In fact, we show that the deformation of the EDL decreases with increase of σ\sigma. The role of hydrodynamic interactions is inferred from direct comparisons to Langevin simulations where the coupling to the LB fluid is switched off. Moreover, systems with divalent counterions are considered. In this case, at high values of σ\sigma the phenomenon of charge inversion is found.Comment: accepted in J. Chem Phys., 10 pages, 9 figure

    Hyperfine interaction and electronic spin fluctuation study on Sr2x_{2-x}Lax_xFeCoO6_6 (x = 0, 1, 2) by high-resolution back-scattering neutron spectroscopy

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    The study of hyperfine interaction by high-resolution inelastic neutron scattering is not very well known compared to the other competing techniques viz. NMR, M\"ossbauer, PACS etc. Also the study is limited mostly to magnetically ordered systems. Here we report such study on Sr2x_{2-x}Lax_xFeCoO6_6 (x = 0, 1, 2) of which first (Sr2_2FeCoO6_6 with x = 0) has a canonical spin spin glass, the second (SrLaFeCoO6_6 with x = 1) has a so-called magnetic glass and the third (La2_2FeCoO6_6 with x = 2) has a magnetically ordered ground state. Our present study revealed clear inelastic signal for SrLaFeCoO6_6, possibly also inelastic signal for Sr2_2FeCoO6_6 below the spin freezing temperatures TsfT_{sf} but no inelastic signal at all for for the magnetically ordered La2_2FeCoO6_6 in the neutron scattering spectra. The broadened inelastic signals observed suggest hyperfine field distribution in the two disordered magnetic glassy systems and no signal for the third compound suggests no or very small hyperfine field at the Co nucleus due to Co electronic moment. For the two magnetic glassy system apart from the hyperfine signal due only to Co, we also observed electronic spin fluctuations probably from both Fe and Co electronic moments. \end{abstract

    Search algorithm for a gravitational wave signal in association with Gamma Ray Burst GRB030329 using the LIGO detectors

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    One of the brightest Gamma Ray Burst ever recorded, GRB030329, occurred during the second science run of the LIGO detectors. At that time, both interferometers at the Hanford, WA LIGO site were in lock and acquiring data. The data collected from the two Hanford detectors was analyzed for the presence of a gravitational wave signal associated with this GRB. This paper presents a detailed description of the search algorithm implemented in the current analysis.Comment: To appear in the Proceedings of 8th Gravitational Wave Data Analysis Workshop (Milwaukee, WI) (Class. Quantum Grav.

    The Critical Coupling Likelihood Method: A new approach for seamless integration of environmental and operating conditions of gravitational wave detectors into gravitational wave searches

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    Any search effort for gravitational waves (GW) using interferometric detectors like LIGO needs to be able to identify if and when noise is coupling into the detector's output signal. The Critical Coupling Likelihood (CCL) method has been developed to characterize potential noise coupling and in the future aid GW search efforts. By testing two hypotheses about pairs of channels, CCL is able to identify undesirable coupled instrumental noise from potential GW candidates. Our preliminary results show that CCL can associate up to 80\sim 80% of observed artifacts with SNR8SNR \geq 8, to local noise sources, while reducing the duty cycle of the instrument by 15\lesssim 15%. An approach like CCL will become increasingly important as GW research moves into the Advanced LIGO era, going from the first GW detection to GW astronomy.Comment: submitted CQ

    Methods for Reducing False Alarms in Searches for Compact Binary Coalescences in LIGO Data

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    The LIGO detectors are sensitive to a variety of noise transients of non-astrophysical origin. Instrumental glitches and environmental disturbances increase the false alarm rate in the searches for gravitational waves. Using times already identified when the interferometers produced data of questionable quality, or when the channels that monitor the interferometer indicated non-stationarity, we have developed techniques to safely and effectively veto false triggers from the compact binary coalescences (CBCs) search pipeline

    Property (RD) for Hecke pairs

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    As the first step towards developing noncommutative geometry over Hecke C*-algebras, we study property (RD) (Rapid Decay) for Hecke pairs. When the subgroup H in a Hecke pair (G,H) is finite, we show that the Hecke pair (G,H) has (RD) if and only if G has (RD). This provides us with a family of examples of Hecke pairs with property (RD). We also adapt Paul Jolissant's works in 1989 to the setting of Hecke C*-algebras and show that when a Hecke pair (G,H) has property (RD), the algebra of rapidly decreasing functions on the set of double cosets is closed under holomorphic functional calculus of the associated (reduced) Hecke C*-algebra. Hence they have the same K_0-groups.Comment: A short note added explaining other methods to prove that the subalgebra of rapidly decreasing functions is smooth. This is the final version as published. The published version is available at: springer.co
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