Preparation of lead (Pb) X-ray fluorescence reference materials for the EPA Pb monitoring program and the IMPROVE network using an aerosol deposition method

X-ray fluorescence (XRF) is a commonly used analytical method to quantify lead (Pb), a toxic element, in atmospheric aerosol. The commercially available reference materials used for calibrating XRF do not mimic the concentrations and filter materials of particulate matter (PM) monitoring networks. In this study, we described an aerosol deposition method to generate Pb reference materials (RMs) over a range of concentrations to serve several purposes for the US Environmental Protection Agency (EPA) and Interagency Monitoring of PROtected Visual Environments (IMPROVE) monitoring networks including laboratory auditing, federal equivalency method evaluation, and calibration and quality control of XRF instruments. The RMs were generated using a laboratory-built aerosol chamber equipped with a federal reference sampler at concentration levels ranging from 0.0125 to 0.70 μg/m³. XRF analysis at UC Davis was demonstrated to be equivalent to a US and EU reference method, inductively coupled plasma—mass spectrometry (ICP-MS), for measuring Pb on RMs following a methodology described in the United States and international standards. The Pb concentrations on subsets of the RMs were verified by three other XRF laboratories with different analyzers and/or quantification methods and were shown to be equivalent to the UC Davis XRF analysis. The generated RMs were demonstrated to have short and long-term stability, satisfying an additional requirement of reference materials.

Copyright © 2016 American Association for Aerosol Research     

Natural convection heat transfer from upward-facing plates in saline water

Saltwater or brackish water is used as a coolant in most industries. Therefore, understanding the heat transfer processes and hydrodynamics during the natural convection in saline water is crucial for enhancing the efficiency of a heat exchanger. This study elaborates on the natural convection heat transfer in saline water under atmospheric conditions. A DC power supply is used to regulate the power given to the heater in a liquid pool for thermal analysis. The pool liquid comprises solutions with varying salinity from 0%, 0.2%, 0.5%, and 2%. The effect of varying salinity on the heat transfer coefficient and the thermal aspects encountered during the desalination process is analyzed. The temperature distribution across the surface of the heater is monitored using an infrared camera. It is studied for the solution of different salinities. The heat transfer coefficient and Nusselt number are investigated during natural convection for normal water and salt solution of different concentrations. It is inferred from the study that in the regime of natural convection, there is no significant difference in the Nusselt number for normal water and saltwater for the lower value of temperature difference between the plate and pool. The heat transfer coefficient in 0.2% saline water is higher as compared to the other solutions.     

Synthesis of cyclic carbonates from carbon dioxide and epoxides using alkali metal halide supported liquid phase catalyst

Using combination of Mn–Co transition metal species with N-hydroxyphthalimide as a catalyst for one-step oxidation of cyclohexane with molecular oxygen in acetic acid at 353 K can give more than 95% selectivity towards oxygenated products with adipic acid as a major product at a high conversion (ca. 78%). A turnover number of 74 for this partial oxidation are also recorded.     

Effect of bark beetle infestation on secondary organic aerosol precursor emissions

Bark beetles are a potentially destructive force in forest ecosystems; however, it is not known how insect attacks affect the atmosphere. The emissions of volatile organic compounds (VOCs) were sampled i.) from bark beetle infested and healthy lodgepole pine (Pinus contorta var. latifolia) trees and ii.) from sites with and without active mountain pine beetle infestation. The emissions from the trunk and the canopy were collected via sorbent traps. After collection, the sorbent traps were extracted with hexane, and the extracts were separated and detected using gas chromatography/mass spectroscopy. Canister samples were also collected and analyzed by a multicolumn gas chromatographic system. The samples from bark beetle infested lodgepole pine trees suggest a 5- to 20-fold enhancement in total VOCs emissions. Furthermore, increases in the β-phellandrene emissions correlated with bark beetle infestation. A shift in the type and the quantity of VOC emissions can be used to identify bark beetle infestation but, more importantly, can lead to increases in secondary organic aerosol from these forests as potent SOA precursors are produced.     

Effect of surfactants on the morphology of titania microspheres prepared by internal gelation process

Internal gelation process was employed for preparation of 0.3–1 mm sized microspheres of titania for their application in ion exchange columns. The conventional internal gelation process was modified by adding surfactant and oil emulsion in the feed broth, which introduced large pores in the structure of the material. The effects of concentration of hydrochloric acid, titanium, surfactant and hexamethylenetetramine to titanium ratio in the feed broth and temperature of calcination on the surface characteristics of the final product were studied. The conditions of preparation were optimized to obtain physically stable porous microspheres suitable for various applications. The resultant material was characterized by pore size distribution, pore volume, thermogravimetry, X-ray diffraction and SEM analyses. Ion exchange behaviour of the material was then studied by pH titration.     

Universal meshes for smooth surfaces with no boundary in three dimensions

We introduce a method to mesh the boundary Γ of a smooth, open domain in immersed in a mesh of tetrahedra. The mesh follows by mapping a specific collection of triangular faces in the mesh to Γ. Two types of surface meshes follow: (a) a mesh that exactly meshes Γ, and (b) meshes that approximate Γ to any order, by interpolating the map over the selected faces; that is, an isoparametric approximation to Γ. The map we use to deform the faces is the closest point projection to Γ. We formulate conditions for the closest point projection to define a homeomorphism between each face and its image. These are conditions on some of the tetrahedra intersected by the boundary, and they essentially state that each such tetrahedron should (a) have a small enough diameter, and (b) have two of its dihedral angles be acute. We provide explicit upper bounds on the mesh size, and these can be computed on the fly. We showcase the quality of the resulting meshes with several numerical examples. More importantly, all surfaces in these examples were meshed with a single background mesh. This is an important feature for problems in which the geometry evolves or changes, because it could be possible for the background mesh to never change as the geometry does. In this case, the background mesh would be a universal mesh 1 for all these geometries. We expect the method introduced here to be the basis for the construction of universal meshes for domains in three dimensions. Copyright © 2016 John Wiley & Sons, Ltd.     

A note on ‘a replenishment policy for items with price-dependent demand,time-proportional deterioration and no shortages’

In a recent paper, Begum et al. (2012 Begum, R., Sahoo, R.R., and Sahu, S.K. (2012), ‘A Replenishment Policy for Items with Price-Dependent Demand, Time-Proportional Deterioration and no Shortages’, International Journal of Systems Science, 43, 903–910.[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar], International Journal of Systems Science, 43, 903–910) established pricing and replenishment policy for an inventory system with price-sensitive demand rate, time-proportional deterioration rate which follows three parameters, Weibull distribution and no shortages. In their model formulation, it is observed that the retailer's stock level reaches zero before the deterioration occurs. Consequently, the model resulted in traditional inventory model with price sensitive demand rate and no shortages. Hence, the main purpose of this note is to modify and present complete model formulation for Begum et al. (2012) Begum, R., Sahoo, R.R., and Sahu, S.K. (2012), ‘A Replenishment Policy for Items with Price-Dependent Demand, Time-Proportional Deterioration and no Shortages’, International Journal of Systems Science, 43, 903–910.[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]. The proposed model is validated by a numerical example and the sensitivity analysis of parameters is carried out.     

An algorithm for triangulating smooth three-dimensional domains immersed in universal meshes

We describe an algorithm to recover a boundary-fitting triangulation for a bounded C²-regular domain immersed in a nonconforming background mesh of tetrahedra. The algorithm consists in identifying a polyhedral domain ω_h bounded by facets in the background mesh and morphing ω_h into a boundary-fitting polyhedral approximation Ω_h of Ω. We discuss assumptions on the regularity of the domain, on element sizes and on specific angles in the background mesh that appear to render the algorithm robust. With the distinctive feature of involving just small perturbations of a few elements of the background mesh that are in the vicinity of the immersed boundary, the algorithm is designed to benefit numerical schemes for simulating free and moving boundary problems. In such problems, it is now possible to immerse an evolving geometry in the same background mesh, called a universal mesh, and recover conforming discretizations for it. In particular, the algorithm entirely avoids remeshing-type operations and its complexity scales approximately linearly with the number of elements in the vicinity of the immersed boundary. We include detailed examples examining its performance.     

Distributed-elementary-source self-regularized dyadic Green's functions for modeling the massloading effect in acoustic devices

A concept for the simulation of two-dimensional models of massive electrodes in micro-acoustic devices has been presented. The method is based on a mesh-less analysis of the underlying boundary value problem. An efficient procedure for the calculation of the involved dyadic Green's functions has been introduced. Major advantage of the proposed method is in the ability of pre-calculating and storing relevant data for the characterization of individual substructures. The latter property is by construction amenable to parallel computing. Glimpse of the numerical results and figures facilitate the discussion of the underlying ideas.