oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Incoherent dynamics in neutron-matter interaction  [PDF]
L. Lanz,B. Vacchini
Physics , 1997, DOI: 10.1103/PhysRevA.56.4826
Abstract: Coherent and incoherent neutron-matter interaction is studied inside a recently introduced approach to subdynamics of a macrosystem. The equation describing the interaction is of the Lindblad type and using the Fermi pseudopotential we show that the commutator term is an optical potential leading to well-known relations in neutron optics. The other terms, usually ignored in optical descriptions and linked to the dynamic structure function of the medium, give an incoherent contribution to the dynamics, which keeps diffuse scattering and attenuation of the coherent beam into account, thus warranting fulfilment of the optical theorem. The relevance of this analysis to experiments in neutron interferometry is briefly discussed.
Influence of the Environment Fluctuations on Incoherent Neutron Scattering Functions  [PDF]
D. J. Bicout
Physics , 2001, DOI: 10.1103/PhysRevE.64.011910
Abstract: In extending the conventional dynamic models, we consider a simple model to account for the environment fluctuations of particle atoms in a protein system and derive the elastic incoherent structure factor (EISF) and the incoherent scattering correlation function C(Q,t) for both the jump dynamics between sites with fluctuating site interspacing and for the diffusion inside a fluctuating sphere. We find that the EISF of the system (or the normalized elastic intensity) is equal to that in the absence of fluctuations averaged over the distribution of site interspacing or sphere radius a. The scattering correlation function is $C(Q,t)=\sum_{n}<{\rm e}^{-\lambda_n(a) t}> \psi(t)$, where the average is taken over the Q-dependent effective distribution of relaxation rates \lambda_n(a) and \psi(t) is the correlation function of the length a. When \psi(t)=1, the relaxation of C(Q,t) is exponential for the jump dynamics between sites (since \lambda_n(a) is independent of a) while it is nonexponential for diffusion inside a sphere.
Polymer and Water Dynamics in Poly(vinyl alcohol)/Poly(methacrylate) Networks. A Molecular Dynamics Simulation and Incoherent Neutron Scattering Investigation  [PDF]
Gaio Paradossi,Ivana Finelli,Francesca Natali,Mark T. F. Telling,Ester Chiessi
Polymers , 2011, DOI: 10.3390/polym3041805
Abstract: Chemically cross-linked polymer networks of poly(vinyl alcohol)/poly(methacrylate) form monolitic hydrogels and microgels suitable for biomedical applications, such as in situ tissue replacement and drug delivery. In this work, molecular dynamics (MD) simulation and incoherent neutron scattering methods are used to study the local polymer dynamics and the polymer induced modification of water properties in poly(vinyl alcohol)/poly(methacrylate) hydrogels. This information is particularly relevant when the diffusion of metabolites and drugs is a requirement for the polymer microgel functionality. MD simulations of an atomic detailed model of the junction domain at the experimental hydration degree were carried out at 283, 293 and 313 K. The polymer-water interaction, the polymer connectivity and the water dynamics were investigated as a function of temperature. Simulation results are compared with findings of elastic and quasi-elastic incoherent neutron scattering measurements, experimental approaches which sample the same space-time window of MD simulations. This combined analysis shows a supercooled water component and an increase of hydrophilicity and mobility with temperature of these amphiphilic polymer networks.
Nitrogen Contamination in Elastic Neutron Scattering  [PDF]
Songxue Chi,Jeffrey W. Lynn,Ying Chen,William Ratcliff II,Benjamin G. Ueland,Nicholas P. Butch,Shanta R. Saha,Kevin Kirshenbaum,Johnpierre Paglione
Physics , 2011, DOI: 10.1088/0957-0233/22/4/047001
Abstract: Nitrogen gas accidentally sealed in a sample container produces various spurious effects in elastic neutron scattering measurements. These effects are systematically investigated and the details of the spurious scattering are presented.
A wave-mechanical model of incoherent neutron scattering II. Role of the momentum transfer  [PDF]
Hans Frauenfelder,Robert D. Young,Paul W. Fenimore
Physics , 2015,
Abstract: We recently introduced a wave-mechanical model for quasi-elastic neutron scattering (QENS) in proteins. We call the model ELM for "Energy Landscape Model". We postulate that the spectrum of the scattered neutrons consists of lines of natural width shifted from the center by fluctuations. ELM is based on two facts: Neutrons are wave packets; proteins have low-lying substates that form the free-energy landscape (FEL). Experiments suggest that the wave packets are a few hundred micrometers long. The interaction between the neutron and a proton in the protein takes place during the transit of the wave packet. The wave packet exerts the force $F(t) = dQ(t)/dt$ on the protein moiety, a part of the protein surrounding the struck proton. $Q(t)$ is the wave vector (momentum) transferred by the neutron wave packet to the proton during the transit. The ensuing energy is stored in the energy landscape and returned to the neutron as the wave packet exits. Kinetic energy thus is changed into potential energy and back. The interaction energy is proportional to $Q$, not to $Q^2$. To develop and check the ELM, we use published work on dehydrated proteins after reversing improper normalizations. In such proteins only vibrations are active and the effects caused by the neutron momentum can be studied undisturbed by external fluctuations. ELM has predictive power. For example it quantitatively predicts the observed inelastic incoherent fraction $S(Q, T)$ over a broad range of temperature and momentum $Q$ with one coefficient if $S(0, T)$ is known.
Biosystems Engineering  [PDF]
E. Gonulol,P. Ulger
Journal of Tekirdag Agricultural Faculty , 2006,
Abstract: Higher agricultural education system has been getting multidiscipline as a result of the level oftechnology, recently. Biosystems Engineering has become popular in developed countries particularly afterelectronic and information technologies has been getting to be a part of agriculture and accompanied ofbiology. In this study definition of Biosystems Engineering discipline, working areas, research, publicationand job opportunities were discussed meticulously. Academic organization of Biosystem Engineering inuniversities and the programs also were explained.
Multiple-scattering effects on incoherent neutron scattering in glasses and viscous liquids  [PDF]
Joachim Wuttke
Physics , 2000, DOI: 10.1103/PhysRevE.62.6531
Abstract: Incoherent neutron scattering experiments are simulated for simple dynamic models: a glass (with a smooth distribution of harmonic vibrations) and a viscous liquid (described by schematic mode-coupling equations). In most situations multiple scattering has little influence upon spectral distributions, but it completely distorts the wavenumber-dependent amplitudes. This explains an anomaly observed in recent experiments.
Neutron-Nucleus Total Elastic Scattering  [PDF]
Cvavb Chandra Raju
Journal of Modern Physics (JMP) , 2015, DOI: 10.4236/jmp.2015.61004
Abstract: Using an exact and complete Yukawa Potential Energy (YPE), the neutron-triton and neutron-helium elastic total scattering cross section is estimated and extrapolated to zero energy. The estimated value agrees pretty well with the experimental value and the procedure can be extended to any neutron-nucleus total scattering. The results are extended to the case of 4He, 7Li, 9Be and 27Al nuclei also.
Elastic and quasi-elastic electron scattering off nuclei with neutron excess  [PDF]
Andrea Meucci,Matteo Vorabbi,Paolo Finelli,Carlotta Giusti,Franco Davide Pacati
Physics , 2013, DOI: 10.1103/PhysRevC.87.054620
Abstract: We present theoretical predictions for electron scattering on oxygen and calcium isotopic chains. The calculations are done within the framework of the distorted-wave Born approximation and the proton and neutron density distributions are evaluated adopting a relativistic Dirac-Hartree model. We present results for the elastic and quasi-elastic cross sections and for the parity-violating asymmetry. As a first step, the results of the models are tested in comparison with some of the data available for elastic and quasi-elastic scattering on 16O and 40Ca nuclei. Then, the evolution of some nuclear properties is investigated as a function of the neutron number. We also present a comparison with the parity-violating asymmetry parameter obtained by the PREX Collaboration on 208Pb and give a prediction for the future experiment CREX on 48Ca.
Proton Elastic Scattering and Neutron Distribution of Unstable Nuclei  [PDF]
K. Kaki,S. Hirenzaki
Physics , 1998, DOI: 10.1142/S0218301399000136
Abstract: We study theoretically how we can determine the neutron density distributions of unstable nuclei from proton elastic scattering. We apply the relativistic impulse model to study the sensitivities of the observables to the density distributionswhich are expressed in Woods-Saxon form. We find that the both radius and diffuseness of densities can be determined from restricted elastic scattering data in principle. We think this result is helpful to design future experiments.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.