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Biomedical subjects

T E Jensen

Publications and source records attributed to T E Jensen.

At least 19 recordsLinked to original sources
PubMed2004

Methane emissions from vehicles.

Methane (CH4) is an important greenhouse gas emitted by vehicles. We report results of a laboratory study of methane emissions using a standard driving cycle for 30 different cars and trucks (1995-1999 model years) from four different manufacturers. We recommend the use of an average emission factor for the U.S. on-road vehicle fleet of (g of CH/g of CO2) = (15 +/- 4) x 10(-5) and estimate that the global vehicle fleet emits 0.45 +/- 0.12 Tg of CH4 yr(-1) (0.34 +/- 0.09 Tg of C yr(-1)), which represents < 0.2% of anthropogenic CH4 emissions. This estimate includes the effects of vehicle aging, cold start, and hot running emissions. The contribution of CH4 emissions from vehicles to radiative forcing of climate change is 0.3-0.4% of that of CO2 emissions from vehicles. The environmental impact of CH4 emissions from vehicles is negligible and is likely to remain so for the foreseeable future.

Air Pollutants↗
PubMed2001

Quantitative analysis of the elemental composition and the mass of bacterial polyphosphate bodies using STEM EDX.

The quantitative analysis of laboratory grown organisms (Plectonema boryanum and Staphylococcus aureus) revealed that a typical in vivo polyphosphate body (PPB) contains O (4.3 x 10(-8) microg), C (1.2 x 10(-8) microg), P (6.7 x 10(-9) microg), Mg (1.3 x 10(-9) microg), Ca (6.7 x 10(-10) microg), K (6.7 x 10(-10) microg), Fe (6.0 x 10(-10) microg), S (5.4 x 10(-10) microg) and Al (5.9 x 10(-10) microg). Quantitative X-ray analysis of samples from nature showed PPB contain O (1.63 x 10(-8) microg), C (4.75 x 10(-9) microg), P (2.50 x 10(-9) microg), Mg (5.0 x 10(-10) microg), Ca (2.50 x 10(-10) microg), K (2.50 x 10(-10) microg), Fe (2.25 x 10(-10) microg) and S (2.0 x 10(-10) microg). The mass of an average polyphosphate body was 6.7 x 10(-8) microg for P. boryanum, 2.5 x 10(-8) microg for S. aureus and for microbes from the natural environment 6.3 x 10(-8) microg. The results indicate that the PPB may have other unknown functions in addition to essential element storage, acting as a detoxification method by sequestering heavy metals and providing a homeostasis system in the cell.

Bacteria↗
PubMed2000

Particle mass emission rates from current-technology, light-duty gasoline vehicles.

Now that the U.S. Environmental Protection Agency has promulgated new National Ambient Air Quality Standards for PM2.5, work will begin on generating the data required to determine the sources of ambient PM2.5 and the magnitude of their contributions to air pollution. This paper summarizes the results of an Environmental Research Consortium program, carried out under the auspices of the U.S. Council for Automotive Research. The program focused on particulate matter (PM) emissions from representative, current-technology, light-duty gasoline vehicles produced by DaimlerChrysler Corp., Ford Motor Co., and General Motors Corp. The vehicles, for the most part taken from the manufacturer's certification and durability fleets, were dynamometer-tested using the three-phase Federal Test Procedure in the companies' laboratories. The test fleet was made up of a mixture of both low-mileage (2K-35K miles) and high-mileage (60K-150K miles) cars, vans, sport utility vehicles, and light trucks. For each vehicle tested, PM emissions were accumulated over 4 cold-start tests, which were run on successive days. PM emission rates from the entire fleet (22 vehicles total) averaged less than 2 mg/mile. All 18 vehicles tested using California Phase 2 reformulated gasoline had PM emission rates less than 2 mg/mile at both low and high mileages.

Air Pollution↗
PubMed1998

Heavy metal uptake by polyphosphate bodies in living and killed cells of Plectonema boryanum (cyanophycae).

The study was conducted to determine whether living or killed cell polyphosphate bodies (PPB) would sequester more of several heavy metals. Living and heat- or glutaraldehyde-killed cells were exposed to 20 ppm of Zn, Pb, Mn and Al. Air-dried cells on Formvar-coated grids were first observed in the transmission electron microscope. The unit was then switched to the scanning transmission mode of operation with the spot setting. X-rays were collected on an energy dispersive X-ray spectrometer and mass fractions of the metals were determined. In all cases live cells sequestered a larger amount of the metal than cells killed by boiling or with glutaraldehyde. In all cases the cells killed by glutaraldehyde sequestered more of the heavy metals than cells killed by boiling. The results of the investigation show that PPB in living cells with active uptake systems take up and sequester more of the metals Zn, Pb, Mn and Al than killed cells.

Absorption↗
PubMed1998

Nickel sequestering by polyphosphate bodies in Staphylococcus aureus.

Metal incorporation and possible cellular compartmentalization of nickel by Staphylococcus aureus was investigated. Cells grown on nutrient agar were removed, washed and exposed to 10, 20, 50 or 100 ppm of nickel in distilled water. The cells were air-dried on Formvar coated grids and then examined in a transmission electron microscope operating in the scanning transmission mode. The spot setting was used in conjunction with an energy dispersive X-ray spectrometer to determine the location and relative amount of the nickel in different parts of the cells. The study showed that polyphosphate bodies bind large amounts of the metal. The peak height for nickel increased in the higher exposure amounts of nickel. No nickel was detected in the cell wall or cytoplasmic areas. The results are discussed in relation to nickel transport in cells and staphylococcal infections in humans.

Microscopy, Electron, Scanning Transmission↗
PubMed1994

The relationship between gasoline composition and vehicle hydrocarbon emissions: a review of current studies and future research needs.

The purpose of this paper is to review current studies concerning the relationship of fuel composition to vehicle engine-out and tail-pipe emissions and to outline future research needed in this area. A number of recent combustion experiments and vehicle studies demonstrated that reformulated gasoline can reduce vehicle engine-out, tail-pipe, running-loss, and evaporative emissions. Some of these studies were extended to understand the fundamental relationships between fuel composition and emissions. To further establish these relationships, it was necessary to develop advanced analytical methods for the qualitative and quantitative analysis of hydrocarbons in fuels and vehicle emissions. The development of real-time techniques such as Fourier transform infrared spectroscopy, laser diode spectroscopy, and atmospheric pressure ionization mass spectrometry were useful in studying the transient behavior of exhaust emissions under various engine operating conditions. Laboratory studies using specific fuels and fuel blends were carried out using pulse flame combustors, single- and multicylinder engines, and vehicle fleets. Chemometric statistical methods were used to analyze the large volumes of emissions data generated from these studies. Models were developed that were able to accurately predict tail-pipe emissions from fuel chemical and physical compositional data. Some of the primary fuel precursors for benzene, 1,3-butadiene, formaldehyde, acetaldehyde and C2-C4 alkene emissions are described. These studies demonstrated that there is a strong relationship between gasoline composition and tail-pipe emissions.

Gasoline↗
PubMed1994

Fine structure of elongate polyhedral bodies (carboxysomes) in two Oscillatoria (Cyanophyceae) isolates.

Polyhedral bodies (carboxysomes) in two Oscillatoria isolates were of two morphological forms. Some were typical polygonal bodies with many straight sides and were approximately 0.2 micron in diameter. Most of the bodies in these isolates were elongate being up to 2.6 microns in length, 33 nm in width and approximately 0.1 micron in depth. Some of the bodies were polygonal with an elongate extension. All of the bodies were limited by a membrane monolayer of approximately 20 A. The function of polyhedral bodies (carboxysomes) is discussed in relation to their observed morphology.

Cyanobacteria↗
PubMed1991

Major antigens in Methylobacterium species and their location in cells using immuno-electron microscopic methods.

This work is a first step in the development of a specific probe for the study of the distribution and colonization of leaf surfaces by pink-pigmented, facultatively methylotrophic (PPFM) bacteria of the genus Methylobacterium. A polyclonal antiserum was produced in rabbits against whole cells of PPFM strain PC1, isolated from surfaces of white clover leaves. Major heat labile antigens were found in extracts of sonicated cells using the Ouchterlony double diffusion method. Very small amounts of a heat stable antigen were also observed. The major antigens were found in extracts of each of fifteen PPFM strains tested but were not found in extracts of other clover heterotrophs nor in extracts of other methylotrophs tested. The distribution of antigens in ultrathin sections of PPFM cells was investigated using PC1 antisera and gold labelled protein A. Gold particles were seen mainly in the outermost layer of the homologous strain, but isolated and washed cell envelopes of strain PC1 like other strains retained very little antigen. Sections of other PPFM strains showed the major antigens were located mainly in the cytoplasm.

Animals↗
PubMed1983

A morphometric study on the effects of ethylene treatment in promoting abscission of tobacco flower pedicels.

The ultrastructural changes observed in ethylene-induced abscission of tobacco flower pedicels (Nicotiana tabacum L. ;Little Turkish') were studied by the techniques of morphometric analysis. The surface area of the membranes, relative volume of the organelles, and the number of organelles were determined for both ethylene-treated and control cells. In pedicels exposed to ethylene for 4.5 to 5 hours, abscission was evident within the separation zone. The most significant change in cell structure was observed in the surface area of the rough endoplasmic reticulum which more than doubled with ethylene treatment of the tissue.

Journal Article↗
PubMed1981

Fine structure of the cell wall of the cyanobacterium Microcoleus vaginatus (Vauch.) Gomont.

The organization of the cell wall of Microcoleus vaginatus (Vauch.) Gomont is described. The four layered wall possesses an unusual layer 2 (mucopolymer containing layer). This layer is 20 nm thick near the crosswall, but abruptly increases in thickness to 90 nm away from the crosswall. In many filaments a perforated sheet 20 nm in thickness was observed on the face of layer 2 which is toward the plasma membrane. It is suggested that this sheet represents an area of mobilization of mucopolymer from layer 2. Electron dense deposits in the cytoplasm or in layer 1 are sometimes observed in association with the developing crosswalls. Junctional pores 12.6 nm in diameter, and spaced 19 nm apart were observed in the longitudinal wall on each side of the junction between the cross and longitudinal walls. Other pores through layer 2 were also observed. These 10 nm pores in the longitudinal wall were randomly arranged (15 to 40 nm apart) and were located on each side of the crosswall up to a distance of 0.6 micrometer from the junction. The relationship between the thickness of layer 2, and the diameter of M. vaginatus and other blue-green algae is discussed.

Cell Wall↗
PubMed1980

Physiological aspects of alkaline phosphatase in selected cyanobacteria.

The alkaline phosphatase of Plectonema boryanum shows a considerable increase in activity following placement of the cells in a phosphate free medium. Five days of phosphate starvation result in a 14-fold increase of alkaline phosphatase activity. Growth in the presence of inhibitors of transcription and translation indicate that the synthesis of the enzyme is de novo. Orthophosphate causes an immediate inhibition of enzyme activity. Enzyme was extracted from P. boryanum with lysozyme or polymyxin B treatment in order to make comparative studies of cell bound and cell free enzyme. Of several enzyme specific inhibitors tested, mercuric chloride was the most effective. Temperature studies showed that the cell bound enzyme was most active at 40 degrees C while the cell free enzyme was most active at 70 degrees C. The pH optimum was 9 for the cell free enzyme, and 8.8 for the cell bound. The enzyme was tested to determine if it could hydrolyse a number of different organic compounds. It hydrolysed p-nitrophenol phosphate 100%, fructose-6-phosphate 45%, beta-glycerol phosphate 25% and other compounds to a lesser degree. Of seventeen other Cyanobacteria tested for alkaline phosphatase, all were positive, and of these eleven were inducible for the enzyme. Ten of the isolates released some of the enzyme into the culture medium. Michaelis constants for the enzyme were also determined.

Alkaline Phosphatase↗
PubMed1979

Effect of ions on the activity of the enzyme alkaline phosphatase from Plectonema boryanum.

Alkaline phosphatase extracted from P. boryanum with lysozyme or polymyxin B treatment was used in a comparative study of cell bound and cell free enzyme. The effects of various ions on enzyme activity were tested. Calcium was found to enhance activity to the greatest degree stimulating the cell bound alkaline phosphatase 100% and cell free enzyme four-fold. Magnesium and potassium also stimulated the activity of cell bound and cell free enzyme. Other ions were found to be inhibitory to varying degrees.

Alkaline Phosphatase↗
PubMed1978

Phosphate metabolism in blue-green bacteria. V. Factors affecting phosphate uptake in Plectonema boryanum.

Plectonema boryanum requires approximately 5 days of exposure to a culture medium lacking phosphorus to induce the "polyphosphate overplus" phenomenon. At pH9, phosphate uptake is greatest both from normal culture medium and from dilute salt solutions. Phosphate uptake from dilute salt solutions was greatest when Na+ or K+ are combined with Ca2+ or Ca2+ and Mg2+. Cells starved of phosphorus in the presence of a high concentration of K+ or Ca2+ in the medium, and then allowed to take up phosphorus under the same conditions, assimilate more phosphorus than with other major ions.

Cyanobacteria↗