The densest amorphous packing of rigid particles is known as random close packing. It has long been appreciated that higher densities are achieved by using collections of particles with a variety of ...sizes. For spheres, the variety of sizes is often quantified by the polydispersity of the particle size distribution: the standard deviation of the radius divided by the mean radius. Several prior studies quantified the increase of the packing density as a function of polydispersity. A particle size distribution is also characterized by its skewness, kurtosis, and higher moments, but the influence of these parameters has not been carefully quantified before. In this work, we numerically generate many sphere packings with different particle radii distributions, varying polydispersity and skewness independently of one another. We find that the packing density can increase significantly with increasing skewness and in some cases skewness can have a larger effect than polydispersity. However, the packing fraction is relatively insensitive to the higher moment value of the kurtosis. We present a simple empirical formula for the value of the random close packing density as a function of polydispersity and skewness.
We study how local rearrangements alter droplet stresses within flowing dense quasi-two-dimensional emulsions at area fractions ϕ≥0.88. Using microscopy, we measure droplet positions while ...simultaneously using their deformed shape to measure droplet stresses. We find that rearrangements alter nearby stresses in a quadrupolar pattern: stresses on neighboring droplets tend to either decrease or increase depending on location. The stress redistribution is more anisotropic with increasing ϕ. The spatial character of the stress redistribution influences where subsequent rearrangements occur. Our results provide direct quantitative support for rheological theories of dense amorphous materials that connect local rearrangements to changes in nearby stress.
Studies of random close packing of spheres have advanced our knowledge about the structure of systems such as liquids, glasses, emulsions, granular media, and amorphous solids. In confined ...geometries, the structural properties of random-packed systems will change. To understand these changes, we study random close packing in finite-sized confined systems, in both two and three dimensions. Each packing consists of a 50-50 binary mixture with particle size ratio of 1.4. The presence of confining walls significantly lowers the overall maximum area fraction (or volume fraction in three dimensions). A simple model is presented, which quantifies the reduction in packing due to wall-induced structure. This wall-induced structure decays rapidly away from the wall, with characteristic length scales comparable to the small particle diameter.
Advances in drug potency and tailored therapeutics are promoting pharmaceutical manufacturing to transition from a traditional batch paradigm to more flexible continuous processing. Here we report ...the development of a multistep continuous-flow CGMP (current good manufacturing practices) process that produced 24 kilograms of prexasertib monolactate monohydrate suitable for use in human clinical trials. Eight continuous unit operations were conducted to produce the target at roughly 3 kilograms per day using small continuous reactors, extractors, evaporators, crystallizers, and filters in laboratory fume hoods. Success was enabled by advances in chemistry, engineering, analytical science, process modeling, and equipment design. Substantial technical and business drivers were identified, which merited the continuous process. The continuous process afforded improved performance and safety relative to batch processes and also improved containment of a highly potent compound.
Abstract
We present techniques to measure fluid flow rates in single- and multi-phase fluid flows by detecting the motion of injected tracers. Our methods exploit acoustic impedance differences ...between liquids and gases to allow one to sense the presence of micron-sized gas bubbles in a liquid when it is irradiated with ultrasonic energy. By cross-correlating signals at multiple locations along the path of flow, the velocity of the moving fluid can be accurately estimated. We report experimental results in single- and two-phase fluid flows and describe the methodologies used in each case that are necessary to enable accurate measurements. In cases of single- and two- phase flows, respectively, flow rates can be measured to less than 5% and less than 10%–15% of known flow rates. While our experiments leveraged differences in acoustic properties, the methods may be generalized to other means of measurement.
We experimentally study the jamming of quasi-two-dimensional emulsions. Our experiments consist of oil-in-water emulsion droplets confined between two parallel plates. From the droplet outlines, we ...can determine the forces between every droplet over a wide range of area fractions
. We study three bidisperse samples that jam at area fractions
c
0.86. Our data show that for
>
c
, the contact numbers and pressure have power-law dependence on
−
c
in agreement with the critical scaling found in numerical simulations. Furthermore, we see a link between the interparticle force law and the exponent for the pressure scaling, supporting prior computational observations. We also observe linear-like force chains (chains of large inter-droplet forces) that extend over 10 particle lengths, and examine the origin of their linearity. We find that the relative orientation of large force segments are random and that the tendency for force chains to be linear is not due to correlations in the direction of neighboring large forces, but instead occurs because the directions are biased towards being linear to balance the forces on each droplet.
We present an experimental technique to measure forces between quasi-2D emulsion droplets to probe the jamming transition.
This paper proposes a novel methodology for 3-D simulations of pressure waves propagating in fluid-filled fractures in an elastic body — the so-called Krauklis waves. The problem is governed by an ...approximation to the compressible Navier–Stokes equations for the viscous fluid in the fracture cavity coupled to the elastic-wave equation in the surrounding solid. The solid is assumed to be isotropic linear elastic and the fluid to be Newtonian. The elastic-wave equation is discretized in space with a quadratic Generalized Finite Element Method (GFEM) and in time by Newmark’s method while the Krauklis waves equations are discretized in space by a quadratic standard FEM and in time by the α-method. A monolithic solver is adopted for the coupled problem and is numerically shown to be stable for the adopted approximation spaces. The GFEM is particularly appealing for the discretization of 3-D fractures since it does not require meshes fitting their geometry. Furthermore, analytical asymptotic solutions are used to enrich the GFEM approximation spaces, increasing the accuracy of the method. Mesh adaptivity around the fracture fronts is employed to further decrease the discretization error while controlling the computational time. The methodology is verified with analytical solutions and compared with experimental data. Different fracture geometries are investigated to demonstrate the complex 3-D effects of the physical phenomenon and the robustness of the proposed GFEM methodology.
•Mesh of proposed GFEM does not need to fit the geometry of fluid-filled fractures.•Singular enrichments and mesh adaptivity lead to an efficient and accurate method.•Method is shown to be stable, and is verified and validated.•Several fracture geometries are analyzed attesting the robustness of the method.•3-D effects are shown to be important even for planar rectangular fractures.
Dynamics of mussel plaque detachment Desmond, Kenneth W; Zacchia, Nicholas A; Waite, J Herbert ...
Soft matter,
2015-Sep-14, Letnik:
11, Številka:
34
Journal Article
Recenzirano
Odprti dostop
Mussels are well known for their ability to generate and maintain strong, long-lasting adhesive bonds under hostile conditions. Many prior studies attribute their adhesive strength to the strong ...chemical interactions between the holdfast and substrate. While chemical interactions are certainly important, adhesive performance is also determined by contact geometry, and understanding the coupling between chemical interactions and the plaque shape and mechanical properties is essential in deploying bioinspired strategies when engineering improved adhesives. To investigate how the shape and mechanical properties of the mussel's plaque contribute to its adhesive performance, we use a custom built load frame capable of fully characterizing the dynamics of the detachment. With this, we can pull on samples along any orientation, while at the same time measuring the resulting force and imaging the bulk deformations of the plaque as well as the holdfast-substrate interface where debonding occurs. We find that the force-induced yielding of the mussel plaque improves the bond strength by two orders of magnitude and that the holdfast shape improves bond strength by an additional order of magnitude as compared to other simple geometries. These results demonstrate that optimizing the contact geometry can play as important a role on adhesive performance as optimizing the chemical interactions as observed in other organisms and model systems.
We experimentally and computationally study the flow of a quasi-two-dimensional emulsion through a constricting hopper shape. Our area fractions are above jamming such that the droplets are always in ...contact with one another and are in many cases highly deformed. At the lowest flow rates, the droplets often clog and thus exit the hopper via intermittent avalanches. At the highest flow rates, the droplets exit continuously. The transition between these two types of behaviors is a fairly smooth function of the mean strain rate. The avalanches are characterized by a power-law distribution of the time interval between droplets exiting the hopper, with long intervals between the avalanches. Our computational studies reproduce the experimental observations by adding a flexible compliance to the system (in other words, a finite stiffness of the sample chamber). The compliance results in continuous flow at high flow rates, and allows the system to clog at low flow rates leading to avalanches. The computational results suggest that the interplay of the flow rate and compliance controls the presence or absence of the avalanches.
We experimentally study the shear flow of oil-in-water emulsion droplets in a thin sample chamber with a hopper shape. In this thin chamber, the droplets are quasi-2D in shape. The sample is at an ...area fraction above jamming and forced to flow with a constant flux rate. Stresses applied to a droplet from its neighbors deform the droplet outline, and this deformation is quantified to provide an
ad hoc
measure of the stress. As the sample flows through the hopper we see large fluctuations of the stress, similar in character to what has been seen in other flows of complex fluids. Periods of time with large decreases in stress are correlated with bursts of elementary rearrangement events ("T1 events" where four droplets rearrange). More specifically, we see a local relationship between these observations: a T1 event decreases the inter-droplet forces up to 3 droplet diameters away from the event. This directly connects microscopic structural changes to macroscopic fluctuations, and confirms theoretical pictures of local rearrangements influencing nearby regions. These local rearrangements are an important means of reducing and redistributing stresses within a flowing material.
Deformation of individual emulsion droplets flowing to the right.
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