Abstract Some textured silicone breast implants with high average surface roughness (‘macrotextured’) have been associated with a rare cancer of the immune system, Breast ImplantAssociated Anaplastic Large Cell Lymphoma (BIAALCL). Silicone elastomer wear debris may lead to chronic inflammation, a key step in the development of this cancer. Here, we model the generation and release of silicone wear debris in the case of a folded implantimplant (‘shellshell’) sliding interface for three different types of implants, characterized by their surface roughness. The ‘smooth’ implant shell with the lowest average surface roughness tested (R a = 2.7 ± 0.6 μ m) resulted in average friction coefficients of μ avg = 0.46 ± 0.11 across 1,000 mm of sliding distance and generated 1,304 particles with an average particle diameter of D avg = 8.3 ± 13.1 μ m. The ‘microtextured’ implant shell (R a = 32 ± 7.0 μ m) exhibited μ avg = 1.20 ± 0.10 and generated 2,730 particles with D avg = 4.7 ± 9.1 μ m. The ‘macrotextured’ implant shell (R a = 80 ± 10 μ m) exhibited the highest friction coefficients, μ avg = 2.82 ± 0.15 and the greatest number of wear debris particles, 11,699, with an average particle size of D avg = 5.3 ± 3.3 μ m. Our data may provide guidance for the design of silicone breast implants with lower surface roughness, lower friction, and smaller quantities of wear debris.
more »
« less
Hopper flows of deformable particles
Numerous experimental and computational studies show that continuous hopper flows of granular materials obey the Beverloo equation that relates the volume flow rate Q and the orifice width w : Q ∼ ( w / σ avg − k ) β , where σ avg is the average particle diameter, kσ avg is an offset where Q ∼ 0, the powerlaw scaling exponent β = d − 1/2, and d is the spatial dimension. Recent studies of hopper flows of deformable particles in different background fluids suggest that the particle stiffness and dissipation mechanism can also strongly affect the powerlaw scaling exponent β . We carry out computational studies of hopper flows of deformable particles with both kinetic friction and background fluid dissipation in two and three dimensions. We show that the exponent β varies continuously with the ratio of the viscous drag to the kinetic friction coefficient, λ = ζ / μ . β = d − 1/2 in the λ → 0 limit and d − 3/2 in the λ → ∞ limit, with a midpoint λ c that depends on the hopper opening angle θ w . We also characterize the spatial structure of the flows and associate changes in spatial structure of the hopper flows to changes in the exponent β . The offset k increases with particle stiffness until k ∼ k max in the hardparticle limit, where k max ∼ 3.5 is larger for λ → ∞ compared to that for λ → 0. Finally, we show that the simulations of hopper flows of deformable particles in the λ → ∞ limit recapitulate the experimental results for quasi2D hopper flows of oil droplets in water.
more »
« less
 NSFPAR ID:
 10400786
 Date Published:
 Journal Name:
 Soft Matter
 Volume:
 18
 Issue:
 42
 ISSN:
 1744683X
 Page Range / eLocation ID:
 8071 to 8086
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
More Like this


null (Ed.)Abstract. This work measured $ \mathrm{d}\sigma/\mathrm{d}\Omega$ d σ / d Ω for neutral kaon photoproduction reactions from threshold up to a c.m. energy of 1855MeV, focussing specifically on the $ \gamma p\rightarrow K^0\Sigma^+$ γ p → K 0 Σ + , $ \gamma n\rightarrow K^0\Lambda$ γ n → K 0 Λ , and $ \gamma n\rightarrow K^0 \Sigma^0$ γ n → K 0 Σ 0 reactions. Our results for $ \gamma n\rightarrow K^0 \Sigma^0$ γ n → K 0 Σ 0 are the firstever measurements for that reaction. These data will provide insight into the properties of $ N^{\ast}$ N * resonances and, in particular, will lead to an improved knowledge about those states that couple only weakly to the $ \pi N$ π N channel. Integrated cross sections were extracted by fitting the differential cross sections for each reaction as a series of Legendre polynomials and our results are compared with prior experimental results and theoretical predictions.more » « less

Beck, R. ; Thiel, A. ; Thoma, U. ; Wunderlich, Y. (Ed.)The BGOOD experiment at the ELSA accelerator facility uses an energy tagged bremsstrahlung photon beam to investigate the excitation structure of the nucleon. The setup consists of a highly segmented BGO calorimeter surrounding the target, with a particle tracking magnetic spectrometer at forward angles. BGOOD is ideal for investigating low momentum transfer processes due to the acceptance and high momentum resolution at forward angles. In particular, this enables the investigation of strangeness photoproduction where tchannel exchange mechanisms play an important role. This also allows access to low momentum exchange kinematics where extended, molecular structure may manifest in reaction mechanisms. First key results at low t indicate a cusplike structure in K + Σ 0 photoproduction at W = 1900 MeV, line shapes and differential cross sections for K + Λ(1405)→ K + Σ 0 π 0 , and a peak structure in K 0 S Σ 0 photoproduction. The peak in the K 0 S Σ 0 channel appears consistent with mesonbaryon generated states, where equivalent models have been used to describe the P C pentaquark candidates in the heavy charmed quark sector.more » « less

We investigate the structural, vibrational, and mechanical properties of jammed packings of deformable particles with shape degrees of freedom in three dimensions (3D). Each 3D deformable particle is modeled as a surfacetriangulated polyhedron, with spherical vertices whose positions are determined by a shapeenergy function with terms that constrain the particle surface area, volume, and curvature, and prevent interparticle overlap. We show that jammed packings of deformable particles without bending energy possess lowfrequency, quartic vibrational modes, whose number decreases with increasing asphericity and matches the number of missing contacts relative to the isostatic value. In contrast, jammed packings of deformable particles with nonzero bending energy are isostatic in 3D, with no quartic modes. We find that the contributions to the eigenmodes of the dynamical matrix from the shape degrees of freedom are significant over the full range of frequency and shape parameters for particles with zero bending energy. We further show that the ensembleaveraged shear modulus 〈 G 〉 scales with pressure P as 〈 G 〉 ∼ P β , with β ≈ 0.75 for jammed packings of deformable particles with zero bending energy. In contrast, β ≈ 0.5 for packings of deformable particles with nonzero bending energy, which matches the value for jammed packings of soft, spherical particles with fixed shape. These studies underscore the importance of incorporating particle deformability and shape change when modeling the properties of jammed soft materials.more » « less

Abstract We study the extent to which divisors of a typical integer n are concentrated. In particular, defining $$\Delta (n) := \max _t \# \{d  n, \log d \in [t,t+1]\}$$ Δ ( n ) : = max t # { d  n , log d ∈ [ t , t + 1 ] } , we show that $$\Delta (n) \geqslant (\log \log n)^{0.35332277\ldots }$$ Δ ( n ) ⩾ ( log log n ) 0.35332277 … for almost all n , a bound we believe to be sharp. This disproves a conjecture of Maier and Tenenbaum. We also prove analogs for the concentration of divisors of a random permutation and of a random polynomial over a finite field. Most of the paper is devoted to a study of the following much more combinatorial problem of independent interest. Pick a random set $${\textbf{A}} \subset {\mathbb {N}}$$ A ⊂ N by selecting i to lie in $${\textbf{A}}$$ A with probability 1/ i . What is the supremum of all exponents $$\beta _k$$ β k such that, almost surely as $$D \rightarrow \infty $$ D → ∞ , some integer is the sum of elements of $${\textbf{A}} \cap [D^{\beta _k}, D]$$ A ∩ [ D β k , D ] in k different ways? We characterise $$\beta _k$$ β k as the solution to a certain optimisation problem over measures on the discrete cube $$\{0,1\}^k$$ { 0 , 1 } k , and obtain lower bounds for $$\beta _k$$ β k which we believe to be asymptotically sharp.more » « less