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Multi-Scale Models to Simulate Interactions between Liquid and Thin Structures
In this dissertation, we introduce a framework for simulating the dynamics between liquid and thin structures, including the effects of buoyancy, drag, capillary cohesion, dripping, and diffusion. After introducing related works, Part I begins with a discussion on the interactions between Newtonian fluid and fabrics. In this discussion, we treat both the fluid and the fabrics as continuum media; thus, the physical model is built from mixture theory. In Part II, we discuss the interactions between Newtonian fluid and hairs. To have more detailed dynamics, we no longer treat the hairs as continuum media. Instead, we treat them as discrete Kirchhoff rods. To deal with the thin layer of liquid that clings to the hairs, we augment each hair strand with a height field representation, through which we introduce a new reduced-dimensional flow model to solve the motion of liquid along the longitudinal direction of each hair. In addition, we develop a faithful model for the hairs' cohesion induced by surface tension, where a penalty force is applied to simulate the collision and cohesion between hairs. To enable the discrete strands interact with continuum-based, shear-dependent liquid, in Part III, we develop models that account for the volume change of the liquid as it passes through strands and the momentum exchange between the strands and the liquid. Accordingly, we extend the reduced-dimensional flow model to simulate liquid with elastoviscoplastic behavior. Furthermore, we use a constraint-based model to replace the penalty-force model to handle contact, which enables an accurate simulation of the frictional and adhesive effects between wet strands. We also present a principled method to preserve the total momentum of a strand and its surface flow, as well as an analytic plastic flow approach for Herschel-Bulkley fluid that enables stable semi-implicit integration at larger time steps.
We demonstrate a wide range of effects, including the challenging animation scenarios involving splashing, wringing, and colliding of wet clothes, as well as flipping of hair, animals shaking, spinning roller brushes from car washes being dunked in water, and intricate hair coalescence effects. For complex liquids, we explore a series of challenging scenarios, including strands interacting with oil paint, mud, cream, melted chocolate, and pasta sauce
Exploring the full parameter space for an interacting dark energy model with recent observations including redshift-space distortions: Application of the parametrized post-Friedmann approach
Dark energy can modify the dynamics of dark matter if there exists a direct
interaction between them. Thus a measurement of the structure growth, e.g.,
redshift-space distortions (RSD), can provide a powerful tool to constrain the
interacting dark energy (IDE) models. For the widely studied model, previous works showed that only a very small coupling
() can survive in current RSD data. However, all
these analyses had to assume and due to the existence of the
large-scale instability in the IDE scenario. In our recent work [Phys. Rev. D
90, 063005 (2014)], we successfully solved this large-scale instability problem
by establishing a parametrized post-Friedmann (PPF) framework for the IDE
scenario. So we, for the first time, have the ability to explore the full
parameter space of the IDE models. In this work, we reexamine the observational
constraints on the model within the PPF framework. By
using the Planck data, the baryon acoustic oscillation data, the JLA sample of
supernovae, and the Hubble constant measurement, we get
(). The fit result becomes
() once we further incorporate the
RSD data in the analysis. The error of is substantially reduced with
the help of the RSD data. Compared with the previous results, our results show
that a negative is favored by current observations, and a relatively
larger interaction rate is permitted by current RSD data.Comment: 12 pages, 3 figure
Probing cosmology with sterile neutrinos via measurements of scale-dependent growth rate of structure
In this paper, we constrain the dimensionless Compton wavelength parameter
of gravity as well as the mass of sterile neutrino by using the
cosmic microwave background observations, the baryon acoustic oscillation
surveys, and the linear growth rate measurements. Since both the model
and the sterile neutrino generally predict scale-dependent growth rates, we
utilize the growth rate data measured in different wavenumber bins with the
theoretical growth rate approximatively scale-independent in each bin. The
employed growth rate data come from the peculiar velocity measurements at
in five wavenumber bins, and the redshift space distortions measurements at
and in one wavenumber bin. By constraining the model
alone, we get a tight 95\% upper limit of . This result is
slightly weakened to (at 2 level) once we
simultaneously constrain the model and the sterile neutrino mass, due to
the degeneracy between the parameters of the two. For the massive sterile
neutrino parameters, we get the effective sterile neutrino mass
eV (2) and the effective
number of relativistic species (2) in the
model. As a comparison, we also obtain
eV (2) and (2) in the standard CDM
model.Comment: 6 pages, 3 figures; revised version accepted for publication in Phys.
Lett.
Measuring growth index in a universe with sterile neutrinos
Consistency tests for the general relativity (GR) can be performed by
constraining the growth index using the measurements of redshift-space
distortions (RSD) in conjunction with other observations. In previous studies,
deviations from the GR expected value of at the
2--3 level were found. In this work, we reconsider the measurement of
in a universe with sterile neutrinos. We constrain the sterile
neutrino cosmological model using the RSD measurements combined with the cosmic
microwave background data (Planck temperature data plus WMAP 9-yr polarization
data), the baryon acoustic oscillation data, the Hubble constant direct
measurement, the Planck Sunyaev-Zeldovich cluster counts data, and the galaxy
shear data. We obtain the constraint result of the growth index,
, well consistent with the GR expected value
(the consistency is at the 0.6 level). For the parameters of sterile
neutrino, we obtain and
eV. We also consider
the BICEP2 data and perform an analysis on the model with tensor modes. Similar
fit results are obtained, showing that once light sterile neutrino is
considered in the universe, GR will become well consistent with the current
observations.Comment: 5 pages, 3 figures; accepted for publication in Physics Letters
Testing models of vacuum energy interacting with cold dark matter
We test the models of vacuum energy interacting with cold dark matter and try
to probe the possible deviation from the CDM model using current
observations. We focus on two specific models, and
. The data combinations come from the Planck 2013 data, the
baryon acoustic oscillations measurements, the type-Ia supernovae data, the
Hubble constant measurement, the redshift space distortions data and the galaxy
weak lensing data. For the model, we find that it can be
tightly constrained by all the data combinations, while for the model, there still exist significant degeneracies between
parameters. The tightest constraints for the coupling constant are
(for ) and
(for ) at the level. For
all the fit results, we find that the null interaction is always
consistent with data. Our work completes the discussion on the interacting dark
energy model in the recent Planck 2015 papers. Considering this work together
with the Planck 2015 results, it is believed that there is no evidence for the
models beyond the standard CDM model from the point of view of
possible interaction.Comment: 7 pages, 2 figures; final version published in Physical Review
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