C and N natural abundance of the soil microbial biomass     

Paul Dijkstra  Ayaka Ishizu  Stephen C. Hart  Egbert Schwartz  Bruce A. Hungate 《Soil biology & biochemistry》2006,38(11):3257-3266

Stable isotope analysis is a powerful tool in the study of soil organic matter formation. It is often observed that more decomposed soil organic matter is ¹³C, and especially ¹⁵N-enriched relative to fresh litter and recent organic matter. We investigated whether this shift in isotope composition relates to the isotope composition of the microbial biomass, an important source for soil organic matter. We developed a new approach to determine the natural abundance C and N isotope composition of the microbial biomass across a broad range of soil types, vegetation, and climates. We found consistently that the soil microbial biomass was ¹⁵N-enriched relative to the total (3.2 ‰) and extractable N pools (3.7 ‰), and ¹³C-enriched relative to the extractable C pool (2.5 ‰). The microbial biomass was also ¹³C-enriched relative to total C for soils that exhibited a C3-plant signature (1.6 ‰), but ¹³C-depleted for soils with a C4 signature (−1.1 ‰). The latter was probably associated with an increase of annual C3 forbs in C4 grasslands after an extreme drought. These findings are in agreement with the proposed contribution of microbial products to the stabilized soil organic matter and may help explain the shift in isotope composition during soil organic matter formation.  相似文献   

Apollo 14 and apollo 16 heavy-particle dosimetry experiments     

Fleischer RL  Hart HR  Comstock GM  Carter M  Renshaw A  Hardy A 《Science (New York, N.Y.)》1973,181(4098):436-438

Doses of heavy particles at positions inside the command modules of Apollo missions 8, 12, 14, and 16 correlate well with the calculated effects of solar modulation of the primary cosmic radiation. Differences in doses at different stowage positions indicate that the redistribution of mass within the spacecraft could enhance safety from the biological damage that would otherwise be expected on manned, deep-space missions.  相似文献   

Mycobacterium tuberculosis in macrophages: effect of certain surfactants and other membrane-active compounds   总被引：10，自引：0，他引：10  

P D Hart 《Science (New York, N.Y.)》1968,162(854):686-689

Some compounds, not directly inhibitory or enhancing, nevertheless influence growth of tubercle bacilli in macrophages in cell culture. They include certain surfactants whose effects can be varied by their structural design. The compounds are probably stored in cell lysosomes. They can interact with various membranes to affect permeability. The anti- and protuberculous surfactants differ in such interaction and also in effect on lysosomal enzyme activity in infected macrophages. A link between the effect on lysosomal membranes and on tuberculous infection is suggested.  相似文献   

Frame-shift deletions in patients with Duchenne and Becker muscular dystrophy   总被引：33，自引：0，他引：33  

S B Malhotra  K A Hart  H J Klamut  N S Thomas  S E Bodrug  A H Burghes  M Bobrow  P S Harper  M W Thompson  P N Ray 《Science (New York, N.Y.)》1988,242(4879):755-759

Duchenne muscular dystrophy (DMD) and its less severe form Becker muscular dystrophy (BMD) are allelic disorders. It has been suggested that in the mutations involving BMD, the translational reading frame of messenger RNA is maintained and a smaller, though partially functional, protein is produced. In order to test this, the exon-intron boundaries of the first ten exons of the DMD gene were determined, and 29 patients were analyzed. In a number of BMD patients (mild and severe BMD), the reading frame of messenger RNA was not maintained. On the basis of these findings, a model for reinitiation from an internal start codon is suggested.  相似文献   

Particle Track, X-ray, Thermal, and Mass Spectrometric Studies of Lunar Material     

Fleischer RL  Haines EL  Hanneman RE  Hart HR  Kasper JS  Lifshin E  Woods RT  Price PB 《Science (New York, N.Y.)》1970,167(3918):568-571

Particle tracks in Apollo 11 samples are dominantly of cosmic ray and solar origin: primary galactic and solar flare particles, likely spallation recoil tracks, and possible solar-wind heavy particles. The energy spectrum of irongroup nuclei is inferred from track density gradients in surface layers, and a limit of < 10(-7) centimeter per year is deduced for the surface erosion rate. From cosmic ray tracks in rock and core samples it is clear that the lunar soil is stirred often during each few million years. X-rays reveal augite, anorthite, olivine, ilmenite, troilite, nonmeteoritic iron, and assorted glasses, but no major structural damage. Hydrogen, helium, and other gases in the fines are compatible with expected solar wind ratios.  相似文献   

Condensation nucleus discriminator making optical measurements on fog: a tool for environmental research     

Hart EJ  Schmidt KH  Vasudevan KN 《Science (New York, N.Y.)》1973,180(4090):1064-1067

An instrument providing a new, rapid, and accurate method of determining the number and critical radii of condensation nuclei with radii under 200 angstroms is described. Based on the principle of the cloud chamber, the instrument measures transient changes in the attenuation and scattering of a monochromatic light beam by the growing fog droplets. From data obtained the absolute number concentration and radii of condensation nuclei can be calculated. Preliminary studies of aerosol formation in beta-irradiated mixtures of air and sulfur dioxide showed that carbon monoxide and methane inhibit the formation of nuclei; relative rate constants can be deduced. Some applications of this instrument for environmental and basic research are pointed out.  相似文献   

The Earth as a seismic absorption band   总被引：1，自引：0，他引：1  

Anderson DL  Kanamori H  Hart RS  Liu HP 《Science (New York, N.Y.)》1977,196(4294):1104-1106

Attenuation of seismic waves indicates that the earth is not perfectly elastic. Dispersion accompanying absorption gives frequency-dependent "elastic" moduli, a fact that must be taken into account when inverting seismic data. Normal mode data are reinverted after correcting for absorption. The correction removes the discrepancy between body wave and free oscillation interpretations of earth structure.  相似文献   

The "corporatization" of science     

Hart DM 《Science (New York, N.Y.)》2002,295(5554):439

  相似文献   

Particle track identification: application of a new technique to apollo helmets     

Fleischer RL  Hart HR  Giard WR 《Science (New York, N.Y.)》1970,170(3963):1189-1191

The Apollo helmets are being used to record the dose of heavy particles to which astronauts are exposed on space missions. An improved method for examining and identifying the etched tracks of heavy charged particles consists of replicating tracks and measuring the etching rate as a function of position along the track. Tracks have been observed in Apollo helmets that correspond to ionized atoms heavier than iron.  相似文献   

Glycosylation of nucleocytoplasmic proteins: signal transduction and O-GlcNAc     

Wells L  Vosseller K  Hart GW 《Science (New York, N.Y.)》2001,291(5512):2376-2378

The dynamic glycosylation of serine or threonine residues on nuclear and cytosolic proteins by O-linked beta-N-acetylglucosamine (O-GlcNAc) is abundant in all multicellular eukaryotes. On several proteins, O-GlcNAc and O-phosphate alternatively occupy the same or adjacent sites, leading to the hypothesis that one function of this saccharide is to transiently block phosphorylation. The diversity of proteins modified by O-GlcNAc implies its importance in many basic cellular and disease processes. Here we systematically examine the current data implicating O-GlcNAc as a regulatory modification important to signal transduction cascades.  相似文献