Predicting particle critical supersaturation from hygroscopic growth measurements in the humified tandem differential mobility analyzer

September 25, 1998.Includes bibliographical references.A new method is described to estimate the critical supersaturation of a quas1- monodisperse, dry particle population composed of pure salts using measurements of hygroscopic growth at several relative humidities below 100%. We describe how Kohler theory may be used to derive two chemical composition dependent parameters, with appropriate accounting for solution effects through a simplified model of the osmotic coefficient. Using a regression routine, the two unknown chemical parameters are derived by fitting the Kohler model to the results from hygroscopic growth experiments. The derived parameters are then used in the Kohler model to calculate critical supersaturations for given dry particle size. From these studies, it is possible to derive the cloud condensation nucleus spectrum if simultaneous measurements of the total number size distribution are made and a sufficient number of critical supersaturations for different particle sizes are determined to characterize the cloud condensation nucleus sub-population of the total particle population. This work represents one of the first, detailed studies on the relationships between particle hygroscopicity and CCN activity using simultaneous measurements of droplet growth and particle critical supersaturation on particles composed of pure salts. In this work we present the theory and methodology that allow the critical supersaturation to be derived from hygroscopic growth measurements, and perform numerical sensitivity studies with respect to assumptions made and anticipated uncertainties in key input parameters to the Kohler model. Laboratory studies are conducted on particles composed of NaCl, (NH4 )2SO 4 , NH4 HSO4 , internally and externally mixed N aC1-(NH4 ) 2SO4 to validate the technique. Studies on ambient particles are also conducted to test if the technique can predict accurate values of Scrit for particles of unknown chemical composition. Results from numerical studies show that for particle diameters of 40 and 100 nm, the maximum errors in critical supersaturations derived using the proposed method are between ±15%. This error is similar to the observed average experimental uncertainty in estimates of the critical supersaturation of -0.6%±11 % determined from CCN studies on particles of known composition. Laboratory studies demonstrate that the critical supersaturation can be derived from hygroscopic growth measurements within experimental uncertainties for the particles of known chemical composition examined in this work. The largest observed differences (-3% to -62%) between HTDMA and CCN derived values of Scrit occurred for ambient particle samples where the chemical composition was unknown and most likely contained a significant amount of hydrophobic material. The numerical and laboratory studies indicate that the proposed technique can establish quantitative relationships between particle size and hygroscopic growth and cloud condensation nucleus activity. The method should help reduce uncertainties in estimates of the indirect effect of particles on climate by allowing more commonly measured aerosol properties, for example particle size and hygroscopic growth, to be directly related to the particle critical supersaturation.Sponsored by the Environmental Protection Agency under graduate student fellowship U-914726-01-0

Master stability functions reveal diffusion-driven pattern formation in networks

We study diffusion-driven pattern-formation in networks of networks, a class of multilayer systems, where different layers have the same topology, but different internal dynamics. Agents are assumed to disperse within a layer by undergoing random walks, while they can be created or destroyed by reactions between or within a layer. We show that the stability of homogeneous steady states can be analyzed with a master stability function approach that reveals a deep analogy between pattern formation in networks and pattern formation in continuous space.For illustration we consider a generalized model of ecological meta-foodwebs. This fairly complex model describes the dispersal of many different species across a region consisting of a network of individual habitats while subject to realistic, nonlinear predator-prey interactions. In this example the method reveals the intricate dependence of the dynamics on the spatial structure. The ability of the proposed approach to deal with this fairly complex system highlights it as a promising tool for ecology and other applications.Comment: 20 pages, 5 figures, to appear in Phys. Rev. E (2018

Electronic structure and Magnetism in BaMn2_2As2_2 and BaMn2_2Sb2_2

We study the properties of ThCr$_2$Si$_2$ structure BaMn$_2$As$_2$ and BaMn$_2$Sb$_2$ using density functional calculations of the electronic and magnetic as well experimental measurements on single crystal samples of BaMn$_2$As$_2$. These materials are local moment magnets with moderate band gap antiferromagnetic semiconducting ground states. The electronic structures show substantial Mn - pnictogen hybridization, which stabilizes an intermediate spin configuration for the nominally $d^5$ Mn. The results are discussed in the context of possible thermoelectric applications and the relationship with the corresponding iron / cobalt / nickel compounds Ba(Fe,Co,Ni)$_2$As$_2$

Geotechnical characterization of the North Ramp of the Exploratory Studies Facility: Yucca Mountain Site Characterization Project. Volume 1, Data summary

This report presents the results of geological and geotechnical characterization of the Miocene volcanic tuff rocks of the Timber Mountain and Paintbrush groups that the tunnel boring machine will encounter during excavation of the Exploratory Studies Facility (ESF) North Ramp. The is being constructed by the DOE as part of the Yucca Mountain Project site characterization activities. The purpose of these activities is to evaluate the feasibility of locating a potential high-level nuclear waste repository on lands adjacent to the Nevada Test Site, Nye County, Nevada. This report was prepared as part of the Soil and Rock Properties Studies in accordance with the 8.3.1.14.2 Study Plan. This report is volume 1 of the data summary

Magnetic, Transport, and Thermal Properties of Single Crystals of the Layered Arsenide BaMn2As2

Growth of BaMn2As2 crystals using both MnAs and Sn fluxes is reported. Room temperature crystallography, anisotropic isothermal magnetization M versus field H and magnetic susceptibility chi versus temperature T, electrical resistivity in the ab plane rho(T), and heat capacity C(T) measurements on the crystals were carried out. The tetragonal ThCr2Si2-type structure of BaMn2As2 is confirmed. After correction for traces of ferromagnetic MnAs impurity phase using M(H) isotherms, the inferred intrinsic chi(T) data of the crystals are anisotropic with chi_{ab}/chi_{c} \approx 7.5 at T = 2 K. The temperature dependences of the anisotropic chi data suggest that BaMn2As2 is a collinear antiferromagnet at room temperature with the easy axis along the c axis, and with an extrapolated Neel temperature T_N \sim 500 K. The rho(T) decreases with decreasing T below 310 K but then increases below \sim 50 K, suggesting that BaMn2As2 is a small band-gap semiconductor with an activation energy of order 0.03 eV. The C(T) data from 2 to 5 K are consistent with this insulating ground state, exhibiting a low temperature Sommerfeld coefficient gamma = 0.0(4) mJ/mol K^2. The Debye temperature is determined from these data to be theta_D = 246(4) K. BaMn2As2 is a potential parent compound for ThCr2Si2-type superconductors.Comment: 7 pages, 6 figures; v2: typos corrected, additional data and discussion, accepted for publication in Phys. Rev.

Two dimensional Dirac fermions and quantum magnetoresistance in CaMnBi2_2

We report two dimensional Dirac fermions and quantum magnetoresistance in single crystals of CaMnBi$_2$. The non-zero Berry's phase, small cyclotron resonant mass and first-principle band structure suggest the existence of the Dirac fermions in the Bi square nets. The in-plane transverse magnetoresistance exhibits a crossover at a critical field $B^*$ from semiclassical weak-field $B^2$ dependence to the high-field unsaturated linear magnetoresistance ($\sim 120$ in 9 T at 2 K) due to the quantum limit of the Dirac fermions. The temperature dependence of $B^*$ satisfies quadratic behavior, which is attributed to the splitting of linear energy dispersion in high field. Our results demonstrate the existence of two dimensional Dirac fermions in CaMnBi$_2$ with Bi square nets.Comment: 5 pages, 4 figure