Biomedical subjects

J O Allen

Publications and source records attributed to J O Allen.

3 recordsLinked to original sources

PubMed2001

Emissions of size-segregated aerosols from on-road vehicles in the Caldecott tunnel.

Particulate matter emissions from the California in-use vehicle fleet were measured as 37,500 vehicles traveled through two bores of the Caldecott Tunnel located in the San Francisco Bay area. Microorifice cascade impactors and filter-based samplers were used to determine the particle chemical composition as a function of particle size. Ammonia emissions from the vehicle fleet were measured as well. Concentrations of aerosol mass, organic carbon, elemental carbon, sulfate ion, nitrate ion, and ammonium ion, as well as 13 elements are reported. The particle mass distribution peaks in the particle size range 0.1-0.18 microm aerodynamic diameter (Da). Elemental carbon and organic matter were the largest components of particle mass in all the size ranges studied. The Caldecott Tunnel bores studied include one which carries light-duty vehicle traffic and one which carries a mixture of light- and heavy-duty vehicle traffic. From experiments conducted in both bores, estimates are made of the size distribution and chemical composition of particulate matter emissions extrapolated to the 100% light-duty and 100% heavy-duty vehicle fleets. The heavy-duty vehicle fleet emitted 1285 +/- 237 mg of fine particulate matter (Da < 1.9 microm)/kg of C contained in the fuel burned (corresponding to approximately 430 +/- 79 mg/km driven). Light-duty vehicles emitted less than 85 +/- 6 mg/kg of C in the fuel burned (corresponding to less than approximately 5.5 +/- 0.4 mg/km driven). Emissions of gas-phase ammonia in the Caldecott Tunnel were measured to be 194 and 267 mg/L of gasoline-equivalent fuel burned in the tunnel. The ammonia emissions are attributed to automobiles that were equipped with 3-way catalysts and operating fuel rich.

Aerosols↗

PubMed2001

Quantification of ATOFMS data by multivariate methods.

Aerosol time-of-flight mass spectrometry (ATOFMS) is capable of measuring the sizes and chemical compositions of individual polydisperse aerosol particles in real time. A qualitative estimate of the particle composition is acquired in the form of a mass spectrum that must be subsequently interpreted in order to draw conclusions regarding atmospheric relevance. The actual problem involves developing a calibration that allows the mass spectral data to be transformed into estimates of the composition of the atmospheric aerosol. A properly calibrated ATOFMS system should be able to quantitatively determine atmospheric concentrations of various species. Ideally, it would be able to accomplish this more rapidly, accurately, with higher size and time resolution, and at a far lower marginal cost than the manual sampling methods that are currently employed. Attempts have already been made at using ATOFMS and similar techniques to extract the bulk chemical species concentration present in an ensemble of particles. This study represents the use of a multivariate calibration method, two-dimensional partial least-squares analysis, for calibrating single-particle mass spectral data. The method presented here is far less labor-intensive than the univariate methods attempted to date and allows for less observer bias. Because of the labor savings, this is also the most comprehensive calibration performed to date, resulting in the quantification of 44 different chemical species.

Aerosols↗

PubMed1994

R-type plasmids in mitochondria from a single source of Zea luxurians teosinte.

Two linear DNA plasmids resembling the R1 and R2 plasmids that are present in the mitochondria of several South American strains of maize were found in mitochondria from a single source of Zea luxurians collected by L. Mazoti. The Mazoti mtDNA is closely related to mtDNAs of other Z. luxurians, but mitochondria derived from the other Z. luxurians sources lack the plasmids. The larger plasmid from Mazoti mitochondria, M1, was cloned and large portions of it were sequenced. Restriction mapping and sequence comparisons showed that approximately 4.9 kb is similar to the S1 plasmid of maize and an additional 2.6 kb is related to R1 sequences integrated into the main mitochondrial genome of N cytoplasm. Therefore, the M1 plasmid appears to be very similar to the R1 plasmid. The inverted repeats at the ends of the M1 plasmid are not identical. The left end IR is similar to the S-TIRs found at the termini of the S plasmids. The right end IR more closely resembles the integrated R1 sequences, including the "variant" region of the TIR. Whereas the variant region contains 13 bp in the S-TIRs and 15 bp in an integrated version of R1, it is 16 bp long in M1. The region of M1 that has no homology to the S1 plasmid is expressed at very low levels in Mazoti and RU cytoplasms, but at much higher levels in CMS-S mitochondria, where part of it is present in the main mitochondrial genome.

Base Sequence↗