The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
J Colmenero - One of the best experts on this subject based on the ideXlab platform.
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single chain Dynamic Structure Factor of linear polymers in an all polymer nano composite
Macromolecules, 2016Co-Authors: Arantxa Arbe, Jose A Pomposo, Isabel Asenjosanz, Debsindhu Bhowmik, Oxana Ivanova, J Kohlbrecher, J ColmeneroAbstract:We present neutron spin echo (NSE) experiments on the single chain Dynamic Structure Factor of long poly(ethylene oxide) (PEO) linear chains in the presence of poly(methyl methacrylate)-based single-chain nanoparticles (SCNPs). A complementary structural characterization of the system discards a significant interpenetration of the components and reveals a close to globular conformation of the SCNPs when surrounded by PEO chains. Analogous NSE measurements on blends of PEO with the linear precursor chains of the SCNPs are taken as a reference for the Dynamics study. For short times (below approximately 5 ns) PEO in both mixtures exhibits slowed down Rouse Dynamics with respect to bulk PEO behavior. The similar deceleration observed in both environments suggests this effect to be due to the large Dynamic asymmetry in the mixtures as evidenced by DSC experiments. More interestingly, the NSE results at longer times reveal a spectacular increase of the explored volume of PEO chains in the all-polymer nanocompo...
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collective features in polyisobutylene a study of the static and Dynamic Structure Factor by molecular Dynamics simulations
Macromolecules, 2014Co-Authors: Yasmin Khairy, F Alvarez, Arantxa Arbe, J ColmeneroAbstract:We present a study of the static and Dynamic Structure Factor of polyisobutylene (PIB) by fully atomistic molecular Dynamics simulations. The reliability of the simulated cell is first assured by c...
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single chain Dynamic Structure Factor of poly ethylene oxide in Dynamically asymmetric blends with poly methyl methacrylate neutron scattering and molecular Dynamics simulations
Macromolecules, 2012Co-Authors: Martin Brodeck, F Alvarez, J Colmenero, Dieter RichterAbstract:We have investigated the Dynamically asymmetric polymer blend composed of short (Mn ≈ 2 kg/mol) poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) chains focusing on the collective Dynamics of the fast PEO component. Using neutron spin-echo (NSE) spectroscopy, the single chain Dynamic Structure Factor of PEO was investigated and compared to results from molecular Dynamics simulations. After a successful validation of the simulations, a thorough analysis of the RPA approximation reveals the composition of the experimentally measured total scattering signal S(Q,t). Using the simulations, we show and calculate two contributions: (1) the relaxation of hydrogenated PEO against deuterated PEO, yielding the single chain Dynamic Structure Factor of PEO, and (2) the relaxation of the PEO component against the PMMA matrix. For the short chains presented here the second contribution shows a significant decay at higher temperatures while it was previously shown that, in the case of long chains, no relaxa...
Xia-ji Liu - One of the best experts on this subject based on the ideXlab platform.
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low momentum Dynamic Structure Factor of a strongly interacting fermi gas at finite temperature the goldstone phonon and its landau damping
Physical Review A, 2018Co-Authors: Peng Zou, Xia-ji LiuAbstract:We develop a microscopic theory of the Dynamic Structure Factor to describe the Bogoliubov-Anderson-Goldstone phonon mode and its damping rate in a strongly interacting Fermi gas at finite temperature. It is based on a density functional approach---the so-called superfluid local density approximation. The accuracy of the theory is quantitatively examined by comparing the theoretical predictions with recent experimental measurements for the local Dynamic Structure Factor of a nearly homogeneous unitary Fermi gas at low transferred momentum [S. Hoinka et al., Nat. Phys. 13, 943 (2017)], without any free parameters. We calculate the Dynamic Structure Factor as functions of temperature and transferred momentum, and determine the temperature evolution of the phonon damping rate, by considering the dominant decay process of the phonon mode via scatterings off fermionic quasiparticles. These predictions can be confronted with future Bragg scattering experiments on a unitary Fermi gas near the superfluid transition.
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low momentum Dynamic Structure Factor of a strongly interacting fermi gas at finite temperature a two fluid hydroDynamic description
Physical Review A, 2018Co-Authors: Peng Zou, Xia-ji LiuAbstract:We provide a description of the Dynamic Structure Factor of a homogeneous unitary Fermi gas at low momentum and low frequency, based on the dissipative two-fluid hydroDynamic theory. The viscous relaxation time is estimated and is used to determine the regime where the hydroDynamic theory is applicable and to understand the nature of sound waves in the density response near the superfluid phase transition. By collecting the best knowledge on the shear viscosity and thermal conductivity known so far, we calculate the various diffusion coefficients and obtain the damping width of the (first and second) sounds. We find that the damping width of the first sound is greatly enhanced across the superfluid transition and very close to the transition the second sound might be resolved in the density response for the transferred momentum up to the half of Fermi momentum. Our work is motivated by the recent measurement of the local Dynamic Structure Factor at low momentum at Swinburne University of Technology and the on-going experiment on sound attenuation of a homogeneous unitary Fermi gas at Massachusetts Institute of Technology. We discuss how the measurement of the velocity and damping width of the sound modes in low-momentum Dynamic Structure Factor may lead to an improved determination of the universal superfluid density, shear viscosity and thermal conductivity of a unitary Fermi gas.
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Dynamic Structure Factor of a strongly correlated fermi superfluid within a density functional theory approach
New Journal of Physics, 2016Co-Authors: Peng Zou, F Dalfovo, Rishi Sharma, Xia-ji LiuAbstract:We theoretically investigate the Dynamic Structure Factor of a strongly interacting Fermi gas at the crossover from Bardeen–Cooper–Schrieffer superfluids to Bose–Einstein condensates, by developing an improved random phase approximation within the framework of a density functional theory (DFT)—the so-called superfluid local density approximation. Compared with the previous random-phase-approximation studies based on the standard Bogoliubov–de Gennes equations, the use of the DFT greatly improves the accuracy of the equation of state at the crossover, and leads to a better description of both collective Bogoliubov-Anderson-Goldstone phonon mode and single-particle fermionic excitations at small transferred momentum. Near unitarity, where the s-wave scattering length diverges, we show that the single-particle excitations start to significantly contribute to the spectrum of Dynamic Structure Factor once the frequency is above a threshold of the energy gap at . The sharp rise in the spectrum at this threshold can be utilized to measure the pairing gap Δ. Together with the sound velocity determined from the phonon branch, the Dynamic Structure Factor provides us some key information of the crossover Fermi superfluid. Our predictions could be examined in experiments with 6Li or 40K atoms using Bragg spectroscopy.
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Dynamic Structure Factor of a strongly correlated fermi superfluid within a density functional theory approach
arXiv: Quantum Gases, 2016Co-Authors: Peng Zou, F Dalfovo, Rishi Sharma, Xia-ji LiuAbstract:We theoretically investigate the Dynamic Structure Factor of a strongly interacting Fermi gas at the crossover from Bardeen-Cooper-Schrieffer superfluids to Bose-Einstein condensates, by developing an improved random phase approximation within the framework of a density functional theory - the so-called superfluid local density approximation. Compared with the previous random-phase-approximation studies based on the standard Bogoliubov-de Gennes equations, the use of the density functional theory greatly improves the accuracy of the equation of state at the crossover, and leads to a better description of both collective Bogoliubov-Anderson-Goldstone phonon mode and single-particle fermionic excitations at small transferred momentum. Near unitarity, where the s-wave scattering length diverges, we show that the single-particle excitations start to significantly contribute to the spectrum of Dynamic Structure Factor once the frequency is above a threshold of the energy gap at $2\Delta$. The sharp rise in the spectrum at this threshold can be utilized to measure the pairing gap $\Delta$. Together with the sound velocity determined from the phonon branch, the Dynamic Structure Factor provides us some key information of the crossover Fermi superfluid. Our predictions could be examined in experiments with $^{6}$Li or $^{40}$K atoms using Bragg spectroscopy.
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Universal Dynamic Structure Factor of a strongly correlated Fermi gas
Physical Review A, 2012Co-Authors: Xia-ji LiuAbstract:Universality of strongly interacting fermions is a topic of great interest in diverse fields. Here we investigate theoretically the universal Dynamic density response of resonantly interacting ultracold Fermi atoms in the limit of either high temperature or large frequency. At high temperature, we use quantum virial expansion to derive universal, nonperturbative expansion functions of the Dynamic Structure Factor; at large momentum, we conjecture that the second-order expansion function gives the Wilson coefficient used in the operator product expansion method. The Dynamic Structure Factor is therefore determined by its second-order expansion function with an overall normalization Factor given by Tan's [S. Tan, Ann. Phys. (NY) 323, 2952 (2008); S. Tan, Ann. Phys. (NY) 323, 2971 (2008); S. Tan, Ann. Phys. (NY) 323, 2987 (2008)] contact parameter. We show that the spin-parallel and -antiparallel Dynamic Structure Factors have, respectively, a tail of the form $\ensuremath{\sim}\ifmmode\pm\else\textpm\fi{}{\ensuremath{\omega}}^{\ensuremath{-}5/2}$ for $\ensuremath{\omega}\ensuremath{\rightarrow}\ensuremath{\infty}$, decaying slower than the total Dynamic Structure Factor found previously ($\ensuremath{\sim}{\ensuremath{\omega}}^{\ensuremath{-}7/2}$). Our predictions for the Dynamic Structure Factor at high temperature or large frequency are testable using Bragg spectroscopy for ultracold atomic Fermi gases.
Roger F. Loring - One of the best experts on this subject based on the ideXlab platform.
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Dynamic Structure Factor IN A BIDISPERSE POLYMER MELT
The Journal of Chemical Physics, 1995Co-Authors: Jeffrey D. Wilson, Roger F. LoringAbstract:We present calculations of the single‐chain Dynamic Structure Factor for a polymer melt composed of linear molecules of the same chemical identity but of two different chain lengths. The fluid is treated within a Dynamical mean‐field approach, in which each molecule is represented as a freely jointed chain moving among stochastic obstacles. The obstacles are of two types, each representing the obstruction of local conformational changes by one of the species present. The obstacle Dynamics are determined self‐consistently by equating the relaxation rate of an obstacle of a given type to the smallest conformational relaxation rate of the species that it represents. Calculation of the Dynamic Structure Factor is mapped onto the solution of a random walk with Dynamical disorder, in which a walker moves on a one‐dimensional lattice with hopping rates that randomly fluctuate among three states. The relevant random walk problem is solved within the effective medium approximation, and the results are employed to examine the dependence of the Dynamic Structure Factor on time, wave vector, chain lengths, and fluid composition.
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Calculation of the Dynamic Structure Factor in polymer melts
The Journal of Chemical Physics, 1994Co-Authors: Avik P. Chatterjee, Roger F. LoringAbstract:In this work, we present calculations of the Dynamic Structure Factor for monodisperse melts of linear polymers. Our calculations are based on a model in which a freely jointed chain encounters fluctuating obstacles whose relaxation is self‐consistently determined from that of the chain conformation. The calculation of the Structure Factor is related to the solution of a one‐dimensional random walk with Dynamical disorder, which is treated within the Dynamical effective medium approximation. This model has been applied previously to the calculation of the self‐diffusion coefficient and the mean‐squared displacement of a chain segment. We present calculations of the Structure Factor over a wide range of wave vectors, times, and entanglement molecular weights. Our predictions are compared with calculations from the theories of Ronca and of de Gennes, and with the experimental results for polyethylene‐butylene‐2 obtained by Richter et al. from neutron spin echo measurements. Our calculations show semiquantit...
Anna Minguzzi - One of the best experts on this subject based on the ideXlab platform.
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Dynamic Structure Factor and drag force in a one dimensional strongly interacting bose gas at finite temperature
Physical Review A, 2015Co-Authors: Guillaume Lang, F W J Hekking, Anna MinguzziAbstract:We study the effect of thermal and quantum fluctuations on the Dynamical response of a one-dimensional, strongly interacting Bose gas in a tight atomic waveguide. We combine the Luttinger liquid theory at arbitrary interactions and the exact Bose-Fermi mapping in the Tonks-Girardeau impenetrable-boson limit to obtain the Dynamic Structure Factor of the strongly interacting fluid at finite temperature. Then we determine the drag force felt by a potential barrier moving along the fluid in the experimentally realistic situation of finite barrier width and temperature.
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Dynamic Structure Factor of one dimensional lattice bosons in a disordered potential a spectral fingerprint of the bose glass phase
New Journal of Physics, 2013Co-Authors: Guillaume Roux, Anna Minguzzi, Tommaso RoscildeAbstract:We study the Dynamic Structure Factor of a one-dimensional Bose gas confined in an optical lattice and modeled by the Bose–Hubbard Hamiltonian, using a variety of numerical and analytical approaches. The Dynamic Structure Factor, experimentally measurable by Bragg spectroscopy, is studied in three relevant cases: in the clean regime, featuring either a superfluid or a Mott phase; and in the presence of two types of (quasi-)disordered external potentials: a quasi-periodic potential obtained from a bichromatic superlattice and a random box disorder—both featuring a Bose-glass phase. In the clean case, we show the emergence of a gapped doublon mode (corresponding to a repulsively bound state) for incommensurate filling, well separated from the low-energy acoustic mode. In the disordered case, we show that the Dynamic Structure Factor provides direct insight into the spatial Structure of the excitations, unveiling their localized nature, which represents a fundamental signature of the Bose-glass phase. Furthermore, it provides a clear fingerprint of the very nature of the localization mechanism which differs for the two kinds of disorder potentials we consider. In special cases, the Dynamic Structure Factor may provide an estimate of the position of the localization transition from superfluid to Bose glass, in a complementary manner to the information deduced from the momentum distribution.
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Dynamic Structure Factor of a superfluid Fermi gas
The European Physical Journal D : Atomic molecular optical and plasma physics, 2001Co-Authors: Anna Minguzzi, Gabriele Ferrari, Yvan CastinAbstract:We describe the excitation spectrum of a two-component neutral Fermi gas in the superfluid phase at finite temperature by deriving a suitable Random-Phase approximation with the technique of functional derivatives. The obtained spectrum for the homogeneous gas at small wavevectors contains the Bogoliubov-Anderson phonon and is essentially different from the spectrum predicted by the static Bogoliubov theory, which instead shows an unphysically large response. We adapt the results for the homogeneous system to obtain the Dynamic Structure Factor of a harmonically confined superfluid and we identify in the spectrum a unique feature of the superfluid phase.
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Dynamic Structure Factor of a superfluid Fermi gas
The European Physical Journal D, 2001Co-Authors: Anna Minguzzi, Gabriele Ferrari, Yvan CastinAbstract:We describe the excitation spectrum of a two-component neutral Fermi gas with attractive interactions in the superfluid phase at finite temperature by deriving a suitable Random-Phase approximation in the collisionless regime with the technique of functional derivatives. The obtained spectrum for the homogeneous gas at small wavevectors contains the Bogoliubov-Anderson phonon and is essentially different from the spectrum predicted by the static Bogoliubov theory, which instead shows an unphysically large response. We adapt the results for the homogeneous system to obtain the Dynamic Structure Factor of a harmonically confined superfluid and we identify in the spectrum a unique feature of the superfluid phase.
Arantxa Arbe - One of the best experts on this subject based on the ideXlab platform.
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single chain Dynamic Structure Factor of linear polymers in an all polymer nano composite
Macromolecules, 2016Co-Authors: Arantxa Arbe, Jose A Pomposo, Isabel Asenjosanz, Debsindhu Bhowmik, Oxana Ivanova, J Kohlbrecher, J ColmeneroAbstract:We present neutron spin echo (NSE) experiments on the single chain Dynamic Structure Factor of long poly(ethylene oxide) (PEO) linear chains in the presence of poly(methyl methacrylate)-based single-chain nanoparticles (SCNPs). A complementary structural characterization of the system discards a significant interpenetration of the components and reveals a close to globular conformation of the SCNPs when surrounded by PEO chains. Analogous NSE measurements on blends of PEO with the linear precursor chains of the SCNPs are taken as a reference for the Dynamics study. For short times (below approximately 5 ns) PEO in both mixtures exhibits slowed down Rouse Dynamics with respect to bulk PEO behavior. The similar deceleration observed in both environments suggests this effect to be due to the large Dynamic asymmetry in the mixtures as evidenced by DSC experiments. More interestingly, the NSE results at longer times reveal a spectacular increase of the explored volume of PEO chains in the all-polymer nanocompo...
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collective features in polyisobutylene a study of the static and Dynamic Structure Factor by molecular Dynamics simulations
Macromolecules, 2014Co-Authors: Yasmin Khairy, F Alvarez, Arantxa Arbe, J ColmeneroAbstract:We present a study of the static and Dynamic Structure Factor of polyisobutylene (PIB) by fully atomistic molecular Dynamics simulations. The reliability of the simulated cell is first assured by c...
