A New Atomic Force Microscopy Technique for the Measurement of the Elastic Properties of Biological Materials

We developed a new technique to measure elastic properties by using the atomic force microscope (AFM) tip to press samples into grooves etched in a GaAs substrate. We measured the Young\u27s modulus of β-chitin fibres with cross-sections less than 40 nm X 20 nm to be 1-2 X 1011 N/m2. In the isotropic approximation, the Young\u27s modulus of the S-layer sheath of the archaeobacterium Methanospirillum hungatei was 1-3 X 1010 N/m2. By testing the sheath to breaking strength we estimated the bacterium can sustain an internal pressure as high as 100-200 atmospheres (1-2 x 107 N/m2)

ACCUMULATION AND RETENTION OF TRITIUM (TRITIATED WATER) IN EMBRYONIC AND LARVAL FISH, AND RADIATION EFFECT.

This report addresses the accumulation and retention of tritium in embryonic and larval fish, and radiation effec

Ability of mononuclear phagocytes from cattle naturally resistant or susceptible to brucellosis to control in vitro intracellular survival of Brucella abortus.

The role of bovine mammary macrophages and peripheral blood monocyte-derived macrophages in natural resistance to bovine brucellosis was evaluated. A group of 11 naturally resistant and 10 chronically infected susceptible cows was studied following challenge with Brucella abortus. Macrophages from a greater proportion (P less than 0.026) of naturally resistant cows were significantly superior to macrophages from susceptible cows in their ability to inhibit the in vitro intracellular replication of B. abortus after challenge exposure. Studies of a second group of cows used mammary macrophages from 12 heifers and blood monocyte-derived macrophages from 22 bulls and heifers. These tests were completed before exposure to B. abortus, using mammary macrophages (P less than 0.039) and blood monocyte-derived macrophages (P less than 0.045), and also showed that macrophages from naturally resistant cattle were significantly superior in their ability to control the in vitro intracellular replication of B. abortus. Our data indicate that the mononuclear phagocytes from more than 80% of the resistant cattle controlled intracellular replication of B. abortus significantly better than did mononuclear phagocytes from susceptible cattle. Mononuclear phagocyte function appears to be an important factor in determining natural resistance to bovine brucellosis

Secular Evolution in Mira Variable Pulsations

Stellar evolution theory predicts that asymptotic giant branch stars undergo a series of short thermal pulses that significantly change their luminosity and mass on timescales of hundreds to thousands of years. Secular changes in these stars resulting from thermal pulses can be detected as measurable changes in period if the star is undergoing Mira pulsations. The American Association of Variable Star Observers (AAVSO) International Database currently contains visual data for over 1500 Mira variables. Light curves for these stars span nearly a century in some cases, making it possible to study the secular evolution of the pulsation behavior on these timescales. In this paper, we present the results of our study of period change in 547 Mira variables using data from the AAVSO. We find non-zero rates of period change, dlnP/dt, at the 2-sigma significance level in 57 of the 547 stars, at the 3-sigma level in 21 stars, and at the level of 6-sigma or greater in eight of the 547. The latter eight stars have been previously noted in the literature, and our derived rates of period changes largely agree with published values. The largest and most statistically significant dlnP/dt are consistent with the rates of period change expected during thermal pulses on the AGB. A number of other stars exhibit non-monotonic period changes on decades-long timescales, the cause of which is not yet known.Comment: 37 pages, with 9 figures and 1 table. The complete electronic version of Table 1 is available from the authors upon request. Accepted for publication in The Astronomical Journa

Studies of enzyme polymorphisms in the Kamuela population of Drosophila mercatorum . II. Evaluation of glycolytic intermediates

A simple and effective cryogenic procedure for the extraction of glycolytic intermediates from whole Drosophila has been developed. This procedure gives consistent results when a measure (µM/liter/OD 260 ) is adopted which corrects for differences in extraction efficiency. Using this measure and a homozygous strain of D. mercatorum , there are no significant differences among extracts for the levels of any of the 15 glycolytic intermediate or energy molecules considered. The profile of means is consistent across experimental designs and instrument types. Coefficients of variation are well below 50% for most variables. The methodology presented has the statistical power to detect a mean change of 10 to 50% using an experimental design which requires as few as 32 observations. The estimated energy charge for resting Drosophila from these studies is the expected value of 0.86.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44142/1/10528_2004_Article_BF00498934.pd