Analysis of laser extracted volatiles in carbonaceous chondrites

It is scientifically important to understand the composition of volatile compounds from interplanetary dust particles (IDPs) because they may be related to the primordial inventory of planetary materials which were necessary to provide environments conducive to the formation of life. The use of a laser microprobe to measure volatiles in IDPs was evaluated. Because primitive meteorites are thought to be closely related to IDPs, carbonaceous chondrites were used for the evaluation. Three sets of experiments were performed to determine the volatiles released from potential substrate materials, to analyze the volatiles released from matrices of bulk samples of carbonaceous chondrites, and to analyze volatiles released from approx. 100 to 200 micron meteorite particles to simulate IDPs. Aluminum appeared to be the best choice of substrate material. Mass ratios between carbonaceous chondrite matrices of Allende and Murchison show fair reproducibility with somewhat high uncertainties. Particles from the Orgueil, Murchison, and Allende meteorites produced measurable quantities of volatiles that appear to have mass spectra comparable to the bulk matrices

Computer image analysis of etched tracks from ionizing radiation

I proposed to continue a cooperative research project with Dr. David S. McKay concerning image analysis of tracks. Last summer we showed that we could measure track densities using the Oxford Instruments eXL computer and software that is attached to an ISI scanning electron microscope (SEM) located in building 31 at JSC. To reduce the dependence on JSC equipment, we proposed to transfer the SEM images to UHCL for analysis. Last summer we developed techniques to use digitized scanning electron micrographs and computer image analysis programs to measure track densities in lunar soil grains. Tracks were formed by highly ionizing solar energetic particles and cosmic rays during near surface exposure on the Moon. The track densities are related to the exposure conditions (depth and time). Distributions of the number of grains as a function of their track densities can reveal the modality of soil maturation. As part of a consortium effort to better understand the maturation of lunar soil and its relation to its infrared reflectance properties, we worked on lunar samples 67701,205 and 61221,134. These samples were etched for a shorter time (6 hours) than last summer's sample and this difference has presented problems for establishing the correct analysis conditions. We used computer counting and measurement of area to obtain preliminary track densities and a track density distribution that we could interpret for sample 67701,205. This sample is a submature soil consisting of approximately 85 percent mature soil mixed with approximately 15 percent immature, but not pristine, soil

Measuring track densities in lunar grains by image analysis

We have developed techniques to use digitized scanning electron micrographs and computer image analysis programs to measure track densities in lunar soil grains. Tracks were formed by highly ionizing solar energetic particles and cosmic rays during near surface exposure on the Moon. The track densities are related to the exposure conditions (depth and time). Distributions of the number of grains as a function of their track densities can reveal the modality of soil maturation. We used a sample that had already been etched in 6 N NaOH at 118 C for 15 h to reveal tracks. We determined that back-scattered electron images taken at 50 percent contrast and approximately 49.8 percent brightness produced suitable high contrast images for analysis. We ascertained gray-scale thresholds of interest: 0-230 for tracks, 231 for masked regions, and 232-255 for background. We found no need to set an upper size limit for distinguishing tracks. We did use lower limits to exclude noise: 16 pixels at 15000x, 4 pixels at 10000x, 2 pixels at 6800x, and 0 pixels at 4600x. We used computer counting and measurement of area to obtain track densities. We found an excellent correlation with manual measurements for track densities below 1x10(exp 8) sq cm. For track densities between 1x10(exp 8) sq cm to 1x10(exp 9) sq cm, we found that a regression formula using the percentage area covered by tracks gave good agreement with manual measurements. Finally we used these new techniques to obtain a track density distribution that gave more detail and was more rapidly obtained than using manual techniques 15 years ago

Image analysis used to count and measure etched tracks from ionizing radiation

We have developed techniques to use digitized scanning electron micrographs and computer image analysis programs to measure track densities in lunar soil grains and plastic dosimeters. Tracks in lunar samples are formed by highly ionizing solar energetic particles and cosmic rays during near surface exposure on the Moon. The track densities are related to the exposure conditions (depth and time). Distributions of the number of grains as a function of their track densities can reveal the modality of soil maturation. We worked on two samples identified for a consortium study of lunar weathering effects, 61221 and 67701. They were prepared by the lunar curator's staff as polished grain mounts that were etched in boiling 1 N NaOH for 6 h to reveal tracks. We determined that backscattered electron images taken at 10 percent contrast and approximately 50 percent brightness produced suitable high contrast images for analysis. We used the NIH Image program to cut out areas that were unsuitable for measurement such as edges, cracks, etc. We ascertained a gray-scale threshold of 25 to separate tracks from background. We used the computer to count everything that was two pixels or greater in size and to measure the area to obtain track densities. We found an excellent correlation with manual measurements for track densities below 1 x 10(exp 8) cm(exp -2). For track densities between 1 x 10(exp 8) cm(exp -2) to 1 x 10(exp 9) cm(exp -2) we found that a regression formula using the percentage area covered by tracks gave good agreement with manual measurements. We determined the track density distributions for 61221 and 67701. Sample 61221 is an immature sample, but not pristine. Sample 67701 is a submature sample that is very close to being fully mature. Because only 10 percent of the grains have track densities less than 10(exp 9) cm(exp -2), it is difficulty to determine whether the sample matured in situ or is a mixture of a mature and a submature soil. Although our analysis of plastic dosimeters is at an early stage of development, results are encouraging. The dosimeter was etched in 6.25 N NaOH at 70 deg C for 16 h. We took 200x secondary electron images of the sample and used the NIH Image software to count and measure major and minor diameters of the etched tracks. We calculated the relative track etch rate from a formula that relates it to the major and minor diameters. We made a histogram of the number of tracks versus their relative etch rate. The relative track etching rate is proportional to the linear energy transfer of the particle. With appropriate calibration experiments, the histogram could be used to calculate the radiation dose

Malaria mosquitoes attracted by fatal fungus.

Insect-killing fungi such as Beauveria bassiana are being evaluated as possible active ingredients for use in novel biopesticides against mosquito vectors that transmit malaria. Fungal pathogens infect through contact and so applications of spores to surfaces such as walls, nets, or other resting sites provide possible routes to infect mosquitoes in and around domestic dwellings. However, some insects can detect and actively avoid fungal spores to reduce infection risk. If true for mosquitoes, such behavior could render the biopesticide approach ineffective. Here we find that the spores of B. bassiana are highly attractive to females of Anopheles stephensi, a major anopheline mosquito vector of human malaria in Asia. We further find that An. stephensi females are preferentially attracted to dead and dying caterpillars infected with B. bassiana, landing on them and subsequently becoming infected with the fungus. Females are also preferentially attracted to cloth sprayed with oil-formulated B. bassiana spores, with 95% of the attracted females becoming infected after a one-minute visit on the cloth. This is the first report of an insect being attracted to a lethal fungal pathogen. The exact mechanisms involved in this behavior remain unclear. Nonetheless, our results indicate that biopesticidal formulations comprising B. bassiana spores will be conducive to attraction and on-source visitation by malaria vectors

<b><i>An. stephensi</i></b> females become infected with <i>B. bassiana</i> following contact with spore-laden caterpillars.74% (34/46) of mosquitoes contacting the sporulating caterpillars vs. 8% (4/47) contacting the uninfected caterpillars exhibited <i>B. bassiana</i> sporulation after death.

<p>N = 46 and 47 females out of 60 tested that contacted the sporulating vs. the healthy-live caterpillars, respectively. Brackets denote ±95% binomial confidence intervals (C.I.). Asterisks indicate a significant difference of infection (***P≤0.001, Chi-square 2×2 test of independence).</p

Basal Metabolic Rate (BMR) measurements showing the mean (± S.E.) amount of CO₂ (ml CO₂/hr/gram of body weight) produced by infected and uninfected <i>Heliothis subflexa</i> fourth instar caterpillars during the days after infection, before they were killed by <i>Beauveria bassiana</i> infection.

<p>GLM was used to examine the difference between treatments (Uninfected and <i>Beauveria</i> infected, N = 7).</p

<i>An. stephensi</i> females are significantly more attracted in Y-tube choice experiments to <i>B. bassiana</i>-infected caterpillars than to uninfected caterpillars, whether they are alive or dead, sporulating or non-sporulating.

<p>(Left) percentage of female <i>An. stephensi</i> flying upwind to cadavers of 4^th-instar <i>H. subflexa</i> caterpillars that were infected with <i>B. bassiana</i> but not sporulating (dark bars) or were uninfected (light bars). (Center) percentage of females flying upwind to cadavers of <i>H. subflexa</i> caterpillars that either exhibited <i>B. bassiana</i> spores (dark bars) or were uninfected (light bars). (Right) percentage flying upwind to <i>B. bassiana</i>-infected but non-sporulating live <i>H. subflexa</i> caterpillars (dark bars) compared to uninfected live caterpillars (light bars). (***P<0.001; Chi-square 2×2 test of independence; N = 90).</p

Dried fungal spores of <i>B. bassiana</i> and <i>M. anisopliae</i> are attractive to female <i>An. stephensi</i>, but spores of <i>B. bassiana</i> are more attractive than those of <i>M. anisopliae</i> or <i>Penicillium</i> spp.

<p><b>A)</b> Percentage of females attracted to 50 mg of dried spores of <i>B. bassiana, M. anisopliae,</i> or <i>Penicillium</i> spp. placed on a filter paper disc (dark bars) versus a blank disc (light bars) (N = 60 females in each comparison); <b>B)</b> Percentage of females attracted to the arm containing <i>B. bassiana</i> spores (dark bars) compared to the arm containing spores of either <i>M. anisopliae</i> or <i>Penicillium</i> (light bars) (N = 60 females in each comparison). Brackets denote ±95% binomial confidence intervals (C.I.). Asterisks indicate significant differences between attraction to treatment choice-pairs (Chi-square 2×2 test of independence; **P≤0.01; ***P≤0.001).</p