46 research outputs found
Creeping motion of a solid particle inside a spherical elastic cavity. II. Asymmetric motion
An analytical method is proposed for computing the low-Reynolds-number
hydrodynamic mobility function of a small colloidal particle asymmetrically
moving inside a large spherical elastic cavity, the membrane of which is
endowed with resistance toward shear and bending. In conjunction with the
results obtained in the first part [Daddi-Moussa-Ider, L\"{o}wen, and Gekle,
Eur. Phys. J. E 41, 104 (2018)], in which the axisymmetric motion normal to the
surface of an elastic cavity is investigated, the general motion for an
arbitrary force direction can be addressed. The elastohydrodynamic problem is
formulated and solved using the classic method of images through expressing the
hydrodynamic flow fields as a multipole expansion involving higher-order
derivatives of the free-space Green's function. In the quasi-steady limit, we
demonstrate that the particle self-mobility function of a particle moving
tangent to the surface of the cavity is larger than that predicted inside a
rigid stationary cavity of equal size. This difference is justified by the fact
that a stationary rigid cavity introduces additional hindrance to the
translational motion of the encapsulated particle, resulting in a reduction of
its hydrodynamic mobility. Furthermore, the motion of the cavity is
investigated, revealing that the translational pair (composite) mobility, which
linearly couples the velocity of the elastic cavity to the force exerted on the
solid particle, is solely determined by membrane shear properties. Our
analytical predictions are favorably compared with fully-resolved computer
simulations based on a completed-double-layer boundary integral method.Comment: 14 pages, 4 figures. This is a pre-print of an article published in
The European Physical Journal E. The final authenticated version is available
online at: https://doi.org/10.1140/epje/i2019-11853-
ASAXS study of CaF2 nanoparticles embedded in a silicate glass matrix
The formation and growth of nanosized CaF2 crystallites by heat treatment of an oxyfluoride glass of composition 7.65Na2O–7.69K2O–10.58CaO–12.5CaF2– 5.77Al2O3–55.8SiO2 (wt%) was investigated using anomalous small-angle X-ray scattering (ASAXS). A recently developed vacuum version of the hybrid pixel detector Pilatus 1M was used for the ASAXS measurements below the Ca K-edge of 4038 eV down to 3800 eV. ASAXS investigation allows the determination of structural parameters such as size and size distribution of nanoparticles and characterizes the spatial distribution of the resonant element, Ca. The method reveals quantitatively that the growing CaF2 crystallites are surrounded by a shell of lower electron density. This depletion shell of growing thickness hinders and finally limits the growth of CaF2 crystallites. Moreover, in samples that were annealed for 10h and more, additional very small heterogeneities (1.6 nm diameter) were found
Membrane penetration and trapping of an active particle
The interaction between nano- or micro-sized particles and cell membranes is
of crucial importance in many biological and biomedical applications such as
drug and gene delivery to cells and tissues. During their cellular uptake, the
particles can pass through cell membranes via passive endocytosis or by active
penetration to reach a target cellular compartment or organelle. In this
manuscript, we develop a simple model to describe the interaction of a
self-driven spherical particle (moving through an effective constant active
force) with a minimal membrane system, allowing for both penetration and
trapping. We numerically calculate the state diagram of this system, the
membrane shape, and its dynamics. In this context, we show that the active
particle may either get trapped near the membrane or penetrates through it,
where the membrane can either be permanently destroyed or recover its initial
shape by self-healing. Additionally, we systematically derive a continuum
description allowing to accurately predict most of our results analytically.
This analytical theory helps identifying the generic aspects of our model,
suggesting that most of its ingredients should apply to a broad range of
membranes, from simple model systems composed of magnetic microparticles to
lipid bilayers. Our results might be useful to predict mechanical properties of
synthetic minimal membranes.Comment: 16 pages, 6 figures. Revised manuscript resubmitted to J. Chem. Phy
Central/eastern North Pacific photochemical precursor distributions for fall/spring seasons as defined by airborne field studies
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95530/1/jgrd9190.pd