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741.
CY Shew C Do K Hong Y Liu L Porcar GS Smith WR Chen 《The Journal of chemical physics》2012,137(2):024907
We present small angle neutron scattering (SANS) measurements of deuterium oxide (D(2)O) solutions of linear and star sodium poly(styrene sulfonate) (NaPSS) as a function of polyelectrolyte concentration. Emphasis is on understanding the dependence of their SANS coherent scattering cross section I(Q) on the molecular architecture of single polyelectrolyte. The key finding is that for a given concentration, star polyelectrolytes exhibit more pronounced characteristic peaks in I(Q), and the position of the first peak occurs at a smaller Q compared to their linear counterparts. Based on a model of integral equation theory, we first compare the SANS experimental I(Q) of salt-free polyelectrolyte solutions with that predicted theoretically. Having seen their satisfactory qualitative agreement, the dependence of counterion association behavior on polyelectrolyte geometry and concentration is further explored. Our predictions reveal that the ionic environment of polyelectrolyte exhibits a strong dependence on polyelectrolyte geometry at lower polyelectrolyte concentration. However, when both linear and star polyelectrolytes exceed their overlap concentrations, the spatial distribution of counterion is found to be essentially insensitive to polyelectrolyte geometry due to the steric effect. 相似文献
742.
Maxwell D. Cummings Tse‐I Lin Lili Hu Abdellah Tahri David McGowan Katie Amssoms Stefaan Last Benoit Devogelaere Marie‐Claude Rouan Leen Vijgen Jan Martin Berke Pascale Dehertogh Els Fransen Erna Cleiren Liesbet vanderHelm Gregory Fanning Kristof VanEmelen Origne Nyanguile Kenny Simmen Pierre Raboisson Sandrine Vendeville 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2012,124(19):4715-4718
743.
Gregory Kennedy Cornelia Chilian Radojko Jaćimović Gašper Žerovnik Luka Snoj Andrej Trkov 《Journal of Radioanalytical and Nuclear Chemistry》2012,291(2):555-559
In order to predict the self-shielding effect in neutron activation of non-spherical samples in reactor neutron spectra, it
is important to know whether the neutron field is sufficiently anisotropic to cause significant variations between horizontal
and vertical sample orientation or with orientation relative to the direction towards the reactor core. Metal wires with significant
neutron self-shielding were irradiated in several channels of the SLOWPOKE reactor at Ecole Polytechnique Montreal and the
TRIGA reactor at the Jožef Stefan Institute. In all cases, the amount of thermal or epithermal self-shielding was found to
be identical, within the experimental uncertainty, regardless of the orientation of the wire, indicating that the neutron
field is essentially isotropic. Models used to predict neutron self-shielding need to be adjusted accordingly. In our Monte
Carlo model, the tube-shaped neutron source was moved back into the moderator and reflecting materials near the sample location
were included, which produced an isotropic neutron field at the sample location. 相似文献
744.
745.
James E. Gentile Gregory J. Davis Samuel S. C. Rund 《Computational & Mathematical Organization Theory》2012,18(4):404-418
Agent-based modeling has been well received in the simulation community. Complex systems are simulated by many autonomous agents whose behavior is defined by a conceptual model. However, the model can be improperly implemented or misinterpreted resulting in an implementation that does not reflect the conceptual rules. It is imperative that the implementation’s function be tested against the model’s expected outcome. In this paper, we present certain steady-state techniques that can be used to verify the operation of agent-based simulations. These methods are introduced and then applied to an ecological model which simulates reproductive dynamics of mosquitoes. 相似文献
746.
We investigate the properties of the zeros of the eigenfunctions on quantum graphs (metric graphs with a Schr?dinger-type differential operator). Using tools such as scattering approach and eigenvalue interlacing inequalities we derive several formulas relating the number of the zeros of the n-th eigenfunction to the spectrum of the graph and of some of its subgraphs. In a special case of the so-called dihedral graph we prove an explicit formula that only uses the lengths of the edges, entirely bypassing the information about the graph??s eigenvalues. The results are explained from the point of view of the dynamics of zeros of the solutions to the scattering problem. 相似文献
747.
Jeffrey Humpherys Gregory Lyng Kevin Zumbrun 《Archive for Rational Mechanics and Analysis》2009,194(3):1029-1079
Extending recent results in the isentropic case, we use a combination of asymptotic ODE estimates and numerical Evans-function
computations to examine the spectral stability of shock-wave solutions of the compressible Navier–Stokes equations with ideal
gas equation of state. Our main results are that, in appropriately rescaled coordinates, the Evans function associated with
the linearized operator about the wave (i) converges in the large-amplitude limit to the Evans function for a limiting shock
profile of the same equations, for which internal energy vanishes at one end state; and (ii) has no unstable (positive real
part) zeros outside a uniform ball |λ| ≦ Λ. Thus, the rescaled eigenvalue ODE for the set of all shock waves, augmented with
the (nonphysical) limiting case, form a compact family of boundary-value problems that can be conveniently investigated numerically.
An extensive numerical Evans-function study yields one-dimensional spectral stability, independent of amplitude, for gas constant
γ in [1.2, 3] and ratio ν/μ of heat conduction to viscosity coefficient within [0.2, 5] (γ ≈ 1.4, ν/μ ≈ 1.47 for air). Other values may be treated similarly but were not considered. The method of analysis extends also to the
multi-dimensional case, a direction that we shall pursue in a future work. 相似文献
748.
We address the problem of making quantitative measurements of local flow velocities in turbulent liquid helium, using tracer
particles. We survey and evaluate presently available particles and previous work to establish the need to develop new particles
for the purpose. We present the first practical solution for visualizing fluid motions using a suspension of solid hydrogen
particles with diameters of about 2 μm. The hydrogen particles can be used to study flows with Taylor-microscale Reynolds
numbers between 85 and 775. The particles can be used equally well with the PIV, LDV, or particle-tracking techniques. 相似文献
749.
We extend previous work on the linear viscoelastic moduli of heterogeneous nematic polymers in a small-amplitude oscillatory
shear flow, focusing on the role of the orientational anchoring conditions at the plates. When tangential or normal anchoring
conditions are applied, the Doi–Marrucci–Greco orientation tensor-flow model effectively reduces to the Leslie–Ericksen director-flow
model, predicting that director distortions control the dynamic moduli with negligible contributions from tensor-order parameters.
In this paper, we examine oblique anchoring angles. We use a combination of analysis and numerical simulation on the generalized
tensor-flow system for arbitrary anchoring conditions to show that any oblique anchoring condition induces a nontrivial order
parameter contribution to the dynamic moduli, which vanishes only in the limit of tangential or normal anchoring. Our approach
reveals that the storage and loss moduli admit an approximate decomposition in terms of two reduced problems that are exactly
solvable: the heterogeneous director–flow response plus the monodomain tensor response to an imposed shear. The importance
of this result is that we gain scaling properties of the moduli with respect to material parameters and experimental conditions
without having to compute and assimilate across the full parameter space. These results provide insight into the relative
importance of the distortional vs bulk nematic elastic stress in determining the viscoelastic moduli, predicting that anchoring
conditions tune the relative contributions. 相似文献
750.
A review of the theory of quasigeostrophic singular vortices embedded in regular flows is presented with emphasis on recent results. The equations governing the joint evolution of singular vortices and regular flow, and the conservation laws (integrals) yielded by these equations are presented. Using these integrals, we prove the nonlinear stability of a vortex pair on the f-plane with respect to any small regular perturbation with finite energy and enstrophy. On the β-plane, a new exact steady-state solution is presented, a hybrid regular-singular modon comprised of a singular vortex and a localized regular component. The unsteady drift of an individual singular β-plane vortex confined to one layer of a two-layer fluid is considered. Analysis of the β-gyres shows that the vortex trajectory is similar to that of a barotropic monopole on the β-plane. Non-stationary behavior of a dipole interacting with a radial flow produced by a point source in a 2D fluid is examined. The dipole always survives after collision with the source and accelerates (decelerates) in a convergent (divergent) radial flow. 相似文献