Edward J. Timm

Pulmonary Retention of Particulate Matter is Associated with Airway Inflammation in Allergic Rats Exposed to Air Pollution in Urban Detroit

A collaborative research study was conducted in order to improve our understanding of the source-to-receptor pathway for ambient fine particulate matter (aerodynamic diameter ≤ 2.5 μ m; PM2.5) and subsequently to investigate the identity and sources of toxic components in PM2.5 responsible for adverse health effects in allergic humans. This research used a Harvard fine particle concentrator to expose Brown Norway rats, with and without ovalbumin-induced allergic airway disease, to concentrated air particles (CAPs) generated from ambient air in an urban Detroit community where the pediatric asthma rate was three times higher than the national average. Rats were exposed to CAPs during the exposure periods in July (mean = 676 μg/m3) and September (313 μg/m3) of 2000. Twenty-four hours after exposures lung lobes were either lavaged with saline to determine cellularity and protein in bronchoalveolar lavage fluid (BALF), or removed for analysis by inductively coupled plasma–mass spectrometry (ICP-MS) to detect ambient PM2.5-derived trace element retention. PM2.5 trace elements of anthropogenic origin, lanthanum (La), vanadium (V), manganese (Mn), and sulfur (S), were recovered from the lung tissues of CAPs-exposed rats. Recovery of those pulmonary anthropogenic particles was further increased in rats with allergic airways. In addition, eosinophils and protein in BALF were increased only in allergic animals exposed to CAPs. These results demonstrate preferential retention in allergic airways of air particulates derived from identified local combustion sources after a short-term exposure. Our findings suggest that the enhancement of allergic airway responses by exposure to PM2.5 is mediated in part by increased pulmonary deposition and localization of potentially toxic elements in urban air.

Temperature-dependent elastic moduli of lead telluride-based thermoelectric materials

In the open literature, reports of mechanical properties are limited for semiconducting thermoelectric materials, including the temperature dependence of elastic moduli. In this study, for both cast ingots and hot-pressed billets of Ag-, Sb-, Sn- and S-doped PbTe thermoelectric materials, resonant ultrasound spectroscopy (RUS) was utilized to determine the temperature dependence of elastic moduli, including Youngs modulus, shear modulus and Poissons ratio. This study is the first to determine the temperature-dependent elastic moduli for these PbTe-based thermoelectrics, and among the few determinations of elasticity of any thermoelectric material for temperatures above 300 K. The Youngs modulus and Poissons ratio, measured from room temperature to 773 K during heating and cooling, agreed well. Also, the observed Youngs modulus, E, versus temperature, T, relationship, E(T) = E 0(1–bT), is consistent with predictions for materials in the range well above the Debye temperature. A nanoindentation study of Youngs modulus on the specimen faces showed that both the cast and hot-pressed specimens were approximately elastically isotropic.

Effects of Concentrated Fine Ambient Particles on Rat Plasma Levels of Asymmetric Dimethylarginine

The health effects of ambient fine particulate matter (PM2.5) and its potential impact on vascular endothelial function have not been thoroughly investigated. As endothelial dysfunction plays an important role in the pathogenesis of atherosclerosis and its complications, we examined the effects of concentrated fine ambient particles (CAPs) on the plasma level of asymmetric dimethylarginine (ADMA) in a pilot study. ADMA is a circulating endogenous inhibitor of nitric oxide synthase (NOS) that is associated with impaired vascular function and increased risk for cardiovascular events. A mobile air research laboratory (AirCARE 1) was used to provide “real-world” CAPs exposures for this study conducted in Detroit, MI. Fourteen Brown Norway rats were exposed to filtered air (FA) (n = 7) or CAPs (0.1–2.5 μm) (n = 7) for 3 consecutive days (8 h/day) in July 2002. Rats were exposed during these periods to average particle mass concentrations of 354 μg/m3. Rat plasma samples were collected 24 h postexposure. Plasma concentrations of ADMA were significantly elevated in rats exposed to CAPs versus those exposed to FA (mean ± standard deviation = 1.49 ± 0.18 vs. 1.29 ± 0.26 μM, p = .05 by one-tailed t-test). Analyses of meteorological data and CAPs trace element composition suggest thatlocal particle emission sources contributed largely to overall mass of CAPs. Results of this pilot study suggest that exposure to PM2.5 at high concentrations may trigger an acute increase in circulating ADMA level. This finding has implications for the regulation of vasomotor tone by particulate pollutants and the propensity for adverse cardiovascular events.

Characterization of dry milled powders of LAST (lead–antimony–silver–tellurium) thermoelectric material

Although thermoelectric (TE) materials are often fabricated as cast ingots, there has been recent interest in the powder processing of these materials. Cast TE materials typically have grain sizes as large as several hundred microns, but powder processing (grinding, milling and then sintering) can produce dense specimens with a reduced grain size, an improved mechanical integrity and enhanced TE properties. In the TE literature when powder processing is employed, little or no description is provided of the powder processing techniques and the powder processing parameters are either not characterized or only a mean particle size is given. In this study, powders milled from solid cast ingots of the TE compound LAST (lead–antimony–silver–tellurium) were characterized via Coulter Counter, to measure the mean powder particle size and the size distribution, scanning electron microscopy (SEM), to examine the powder particle morphology, and X-ray diffraction (XRD), to detect possible phase changes or amorphization. The impurity levels in the milled powders were examined by wear rate measurements on the milling media, as well as by energy dispersive X-ray analysis and inductively coupled plasma measurements.

Young's modulus as a function of composition for an n-type lead-antimony-silver-telluride (LAST) thermoelectric material

For 17 cast lead–antimony–silver–telluride (LAST) thermoelectric specimens (representing 14 different chemical compositions), a combination of Vickers and Knoop microindentation techniques were used to determine the composition-dependent Youngs modulus, E, which ranged from 24 to 68 GPa. Following microindentation, independent nanoindentation measurements were also performed on 10 of the 17 specimens. In the literature, for pseudobinary joins in ternary or quaternary compounds (with the compositions A x B1– x C or A x B1– x CD, respectively), changes in the Youngs modulus have been expressed as quadratic functions of the compositional parameter x. In this study, we extend the quadratic functional form to a paraboloid in four composition variables to describe composition-dependent changes in E for the LAST compounds. Also, the composition-dependent changes in LAST are compared to the trends observed in the literature for E and bulk modulus for systems described by a single compositional variable.

Weibull analysis of the biaxial fracture strength of a cast p-type LAST-T thermoelectric material

This is the first study applying Weibull statistics to the strength distribution of a thermoelectric (TE) material and to determine the fracture strength of a member of the LAST-T (lead–antimony–silver–tellurium–tin) family of high-temperature TE compounds. The p-type TE material Ag0.9Pb9Sn9Sb0.6Te20 was cast from the melt and specimens cut from the resulting ingot were fractured in a ball-on-ring biaxial fracture test. The Weibull parameters (characteristic strength and Weibull modulus) were obtained from the fracture data. Implications of the Weibull analysis on the fabrication of TE devices are discussed.

The Measurement and Control of Cyclic Variations of Flow in a Piston Cylinder Assembly

The existence of the cyclic variation of the flow inside an cylinder affects the performance of the engine. Developing methods to understand and control in-cylinder flow has been a goal of engine designers for nearly 100 years. In this paper, passive control of the intake flow of a 3.5-liter DaimlerChrysler engine was examined using a unique optical diagnostic technique: Molecular Tagging Velocimetry (MTV), which has been developed at Michigan State University. Probability density functions (PDFs) of the normalized circulation are calculated from instantaneous planar velocity measurements to quantify gas motion within a cylinder. Emphasis of this work is examination of methods that quantify the cyclic variability of the flow. In addition, the turbulent kinetic energy (TKE) of the flow on the tumble and swirl plane is calculated and compared to the PDF circulation results.

Mechanical characterization of PbTe-based thermoelectric materials

PbTe-based thermoelectric (TE) materials exhibit promising thermoelectric properties and have potential applications in waste heat recovery from sources such as truck engines and shipboard engines. TE components designed for these applications will be subject to mechanical/thermal loading and vibration as a result from in-service conditions, including mechanical vibration, mechanical and/or thermal cycling, and thermal shock. In the current study, we present and discuss the mechanical properties of several PbTe-based compositions with different dopants and processing methods, including n-type and p-type specimens fabricated both by casting and by powder processing. Room temperature hardness and Youngs modulus are studied by Vickers indentation and nanoindentation while fracture strength is obtained by biaxial flexure testing. Temperature dependent Youngs modulus, shear modulus, and Poissons ratio are studied via resonant ultrasound spectroscopy (RUS).

Temperature-dependent thermal expansion of cast and hot-pressed LAST (Pb–Sb–Ag–Te) thermoelectric materials

The thermal expansion for two compositions of cast and hot-pressed LAST (Pb–Sb–Ag–Te) n-type thermoelectric materials has been measured between room temperature and 673 K via thermomechanical analysis (TMA). In addition, using high-temperature X-ray diffraction (HT-XRD), the thermal expansion for both cast and hot-pressed LAST materials was determined from the temperature-dependent lattice parameters measured between room temperature and 623 K. The TMA and HT-XRD determined values of the coefficient of thermal expansion (CTE) for the LAST compositions ranged between 20 × 10−6 K−1 and 24 × 10−6 K−1, which is comparable to the CTE values for other thermoelectric materials including PbTe and Bi2Te3. The CTE of the LAST specimens with a higher Ag content (Ag0.86Pb19Sb1.0Te20) exhibited a higher CTE value than that of the LAST material with a lower Ag content (Ag0.43Pb18Sb1.2Te20). In addition, a peak in the temperature-dependent CTE was observed between room temperature and approximately 450 K for both the cast and hot-pressed LAST with the Ag0.86Pb19Sb1.0Te20 composition, whereas the CTE of the Ag0.43Pb18Sb1.2Te20 specimen increased monotonically with temperature.

Room-temperature mechanical properties of LAST (Pb–Sb–Ag–Te) thermoelectric materials as a function of cooling rate during ingot casting

In this study, we focus on the room-temperature mechanical properties of LAST (Pb–Sb–Ag–Te) materials fabricated using casting with slow-cool temperature profiles (cooling rate <5°C h−1) including biaxial flexural strength, indentation hardness, Youngs modulus, and dynamic elastic moduli. The slow-cooled specimens exhibited values of Youngs modulus and hardness that are comparable to those of previously reported fast-cooled LAST materials (cooling rate >5°C h−1). The higher biaxial flexural strength is potentially beneficial for the mechanical integrity of thermoelectric devices.