Self Assembled Clusters of Spheres Related to Spherical Codes

We consider the thermodynamically driven self-assembly of spheres onto the surface of a central sphere. This assembly process forms self-limiting, or terminal, anisotropic clusters (N-clusters) with well defined structures. We use Brownian dynamics to model the assembly of N-clusters varying in size from two to twelve outer spheres, and free energy calculations to predict the expected cluster sizes and shapes as a function of temperature and inner particle diameter. We show that the arrangements of outer spheres at finite temperatures are related to spherical codes, an ideal mathematical sequence of points corresponding to densest possible sphere packings. We demonstrate that temperature and the ratio of the diameters of the inner and outer spheres dictate cluster morphology and dynamics. We find that some N-clusters exhibit collective particle rearrangements, and these collective modes are unique to a given cluster size N. We present a surprising result for the equilibrium structure of a 5-cluster, which prefers an asymmetric square pyramid arrangement over a more symmetric arrangement. Our results suggest a promising way to assemble anisotropic building blocks from constituent colloidal spheres.Comment: 15 pages, 10 figure

Nonlinear Machine Learning and Design of Reconfigurable Digital Colloids

Digital colloids, a cluster of freely rotating “halo particles tethered to the surface of a central particle, were recently proposed as ultra-high density memory elements for information storage. Rational design of these digital colloids for memory storage applications requires a quantitative understanding of the thermodynamic and kinetic stability of the configurational states within which information is stored. We apply nonlinear machine learning to Brownian dynamics simulations of these digital colloids to extract the low-dimensional intrinsic manifold governing digital colloid morphology, thermodynamics, and kinetics. By modulating the relative size ratio between halo particles and central particles, we investigate the size-dependent configurational stability and transition kinetics for the 2-state tetrahedral (N=4) and 30-state octahedral (N=6) digital colloids. We demonstrate the use of this framework to guide the rational design of a memory storage element to hold a block of text that trades off the competing design criteria of memory addressability and volatility

Optimal Filling of Shapes

We present filling as a type of spatial subdivision problem similar to covering and packing. Filling addresses the optimal placement of overlapping objects lying entirely inside an arbitrary shape so as to cover the most interior volume. In n-dimensional space, if the objects are polydisperse n-balls, we show that solutions correspond to sets of maximal n-balls. For polygons, we provide a heuristic for finding solutions of maximal discs. We consider the properties of ideal distributions of N discs as N approaches infinity. We note an analogy with energy landscapes.Comment: 5 page

Rigid body constraints realized in massively-parallel molecular dynamics on graphics processing units,

Molecular dynamics (MD) methods compute the trajectory of a system of point particles in response to a potential function by numerically integrating Newton's equations of motion. Extending these basic methods with rigid body constraints enables composite particles with complex shapes such as anisotropic nanoparticles, grains, molecules, and rigid proteins to be modeled. Rigid body constraints are added to the GPU-accelerated MD package, HOOMD-blue, version 0.10.0. The software can now simulate systems of particles, rigid bodies, or mixed systems in microcanonical (NVE), canonical (NVT), and isothermalisobaric (NPT) ensembles. It can also apply the FIRE energy minimization technique to these systems. In this paper, we detail the massively parallel scheme that implements these algorithms and discuss how our design is tuned for the maximum possible performance. Two different case studies are included to demonstrate the performance attained, patchy spheres and tethered nanorods. In typical cases, HOOMDblue on a single GTX 480 executes 2.5-3.6 times faster than LAMMPS executing the same simulation on any number of CPU cores in parallel. Simulations with rigid bodies may now be run with larger systems and for longer time scales on a single workstation than was previously even possible on large clusters

The Ursinus Weekly, October 21, 1977

Ursinus news in brief: Espada speaks at conference; Ursinus Homecoming; Buy a slave! • Craft elected as officer • New dining style proves popular • Board to vote on calendar • Students experience new dining style • Student employment remains stable • Comment: Student involvement; On cocktail grading • Letters to the editor • 1.2 million raised: Advance Ursinus first year • The Power behind Ursinus mediocrity • Homecoming candidates • Ursinus and the first digital computer • Bears finally come out of the woods • Varsity & JV hockey • C.C. 7-1! • 3 & 4: All wins • Volleyball: Dig it! • Bears winhttps://digitalcommons.ursinus.edu/weekly/1073/thumbnail.jp

Treatability Study of In Situ Technologies for Remediation of Hexavalent Chromium in Groundwater at the Puchack Well Field Superfund Site, New Jersey

This treatability study was conducted by Pacific Northwest National Laboratory (PNNL), at the request of the U. S. Environmental Protection Agency (EPA) Region 2, to evaluate the feasibility of using in situ treatment technologies for chromate reduction and immobilization at the Puchack Well Field Superfund Site in Pennsauken Township, New Jersey. In addition to in situ reductive treatments, which included the evaluation of both abiotic and biotic reduction of Puchack aquifer sediments, natural attenuation mechanisms were evaluated (i.e., chromate adsorption and reduction). Chromate exhibited typical anionic adsorption behavior, with greater adsorption at lower pH, at lower chromate concentration, and at lower concentrations of other competing anions. In particular, sulfate (at 50 mg/L) suppressed chromate adsorption by up to 50%. Chromate adsorption was not influenced by inorganic colloids

Hanford 100N Area Apatite Emplacement: Laboratory Results of Ca-Citrate-PO4 Solution Injection and Sr-90 Immobilization in 100N Sediments

This report summarizes laboratory scale studies investigating the remediation of Sr-90 by Ca-citrate-PO4 solution injection/infiltration to support field injection activities in the Hanford 100N area. This study is focused on experimentally testing whether this remediation technology can be effective under field scale conditions to mitigate Sr-90 migration 100N area sediments into the Columbia River. Sr-90 is found primarily adsorbed to sediments by ion exchange (99% adsorbed, < 1% in groundwater) in the upper portion of the unconfined aquifer and lower vadose zone. Although primarily adsorbed, Sr-90 is still considered a high mobility risk as it is mobilized by seasonal river stage increases and by plumes of higher ionic strength relative to groundwater. This remediation technology relies upon the Ca-citrate-PO4 solution forming apatite precipitate [Ca6(PO4)10(OH)2], which incorporates some Sr-90 during initial precipitation and additionally slowly incorporates Sr-90 by solid phase substitution for Ca. Sr substitution occurs because Sr-apatite is thermodynamically more stable than Ca-apatite. Once the Sr-90 is in the apatite structure, Sr-90 will decay to Y-90 (29.1 y half-life) then Zr-90 (64.1 h half-life) without the potential for migration into the Columbia River. For this technology to be effective, sufficient apatite needs to be emplaced in sediments to incorporate Sr and Sr-90 for 300 years (~10 half-lives of Sr-90), and the rate of incorporation needs to exceed the natural groundwater flux rate of Sr in the 100N area. A primary objective of this study is to supply an injection sequence to deliver sufficient apatite into subsurface sediments that minimizes initial mobility of Sr-90, which occurs because the injection solution has a higher ionic strength compared to groundwater. This can be accomplished by sequential injections of low, then high concentration injection of Ca-citrate-PO4 solutions. Assessment of low concentration Ca-citrate-PO4, citrate-PO4, and PO4 solutions show greater Sr and Sr-90 incorporation during initial precipitation and less initial mobilization with solutions with low Ca2+ concentration. While all solutions showed nearly the same Sr uptake into apatite (14 to 17% by 2 weeks, 21% to 30% by 5 weeks), the incorporation efficiency (i.e., mM Sr incorporated per mM PO4 injected) was higher for solutions containing citrate. The Sr incorporation rate into apatite during initial precipitation (by 1 month) averaged 4.64 ± 1.9 x 10-4 h-1 (half-life 1500 ± 430 h, 8.85 x 10-7 mg Sr/day/mg apatite). The injection solution used in field injections #3 to #18 (10 mM PO4, 1 mM Ca, 2.5 mM citrate), which is deficient in Ca (a total of 16.7 mM needed to form apatite with 10 mM of PO4), resulted in the initial Sr and Ca peak (24 h) at 4.7x groundwater. By 30 days, the aqueous Sr concentration was 0.28x groundwater and Ca 0.43x groundwater, as both Sr and Ca are used to form initial apatite precipitates. Reactive transport simulation of the complex ion exchange, biodegradation, and precipitation processes showed that the initial Sr groundwater increase mobilized only 1.5% of the Sr mass in sediments. Citrate biodegradation, a necessary step in Ca-citrate-PO4 solutions forming apatite, had an average half-life of 50 h (at aquifer sediment/water ratio and temperature), and decreased an order of magnitude with sediment depth as the microbial biomass decreased five orders of magnitude. The rate of citrate biodegradation was relatively invariant with biomass and water saturation (50% to 100%, for vadose zone infiltration) possibly due to significant microbial injection using river water and subsurface microbial mobilization

Infant Outcomes Following Maternal Infection With Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2): First Report From the Pregnancy Coronavirus Outcomes Registry (PRIORITY) Study.

Infant outcomes after maternal severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection are not well described. In a prospective US registry of 263 infants, maternal SARS-CoV-2 status was not associated with birth weight, difficulty breathing, apnea, or upper or lower respiratory infection through 8 weeks of age