342 research outputs found
The muon content of EAS as a function of primary energy
The muon content of extensive air showers (EAS) was measured over the wide primary energy range 10 to the 16th power to 10 to the 20th power eV. It is reported that the relative muon content of EAS decreases smoothly over the energy range 10 to the 17th power to 10 to the 19th power eV and concluded that the primary cosmic ray flux has a constant mass composition over this range. It is also reported that an apparent significant change in the power index occurs below 10 to the 17th power eV rho sub c (250 m) sup 0.78. Such a change indicates a significant change in primary mass composition in this range. The earlier conclusions concerning EAS of energy 10 to the 17th power eV are confirmed. Analysis of data in the 10 to the 16th power - 10 to the 17th power eV range revealed a previously overlooked selection bias in the data set. The full analysis of the complete data set in the energy range 10 to the 16th power - 10 to the 17th power ev with the selection bias eliminated is presented
Spatial mode detection by frequency upconversion
The efficient creation and detection of spatial modes of light has become
topical of late, driven by the need to increase photon-bit-rates in classical
and quantum communications. Such mode creation/detection is traditionally
achieved with tools based on linear optics. Here we put forward a new spatial
mode detection technique based on the nonlinear optical process of
sum-frequency generation. We outline the concept theoretically and demonstrate
it experimentally with intense laser beams carrying orbital angular momentum
and Hermite-Gaussian modes. Finally, we show that the method can be used to
transfer an image from the infrared band to the visible, which implies the
efficient conversion of many spatial modes.Comment: Published version, 4 pages, 5 figure
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Hydropyrolysis of high molecular weight organic matter in Murchison
Hydropyrolysis of the Murchison macromolecular material releases polyaromatic compounds including phenanthrene, carbazole, fluoranthene, pyrene, chrysene, perylene, benzoperylene and coronene units with varying degrees of alklyation
Extraterrestrial nucleobases in the Murchison meteorite
Carbon-rich meteorites, carbonaceous chondrites, contain many biologically
relevant organic molecules and delivered prebiotic material to the young Earth.
We present compound-specific carbon isotope data indicating that measured
purine and pyrimidine compounds are indigenous components of the Murchison
meteorite. Carbon isotope ratios for uracil and xanthine of delta13C=+44.5per
mil and +37.7per mil, respectively, indicate a non-terrestrial origin for these
compounds. These new results demonstrate that organic compounds, which are
components of the genetic code in modern biochemistry, were already present in
the early solar system and may have played a key role in life's origin.Comment: 31 pages, 4 figures, 3 table
The potential science and engineering value of samples delivered to Earth by Mars sample return
Executive summary provided in lieu of abstract
Characteristics of fine and ultrafine aerosols in the London underground.
Underground railway systems are recognised spaces of increased personal pollution exposure. We studied the number-size distribution and physico-chemical characteristics of ultrafine (PM0.1), fine (PM0.1-2.5) and coarse (PM2.5-10) particles collected on a London underground platform. Particle number concentrations gradually increased throughout the day, with a maximum concentration between 18:00 h and 21:00 h (local time). There was a maximum decrease in mass for the PM2.5, PM2.5-10 and black carbon of 3.9, 4.5 and ~ 21-times, respectively, between operable (OpHrs) and non-operable (N-OpHrs) hours. Average PM10 (52 ÎŒg m-3) and PM2.5 (34 ÎŒg m-3) concentrations over the full data showed levels above the World Health Organization Air Quality Guidelines. Respiratory deposition doses of particle number and mass concentrations were calculated and found to be two- and four-times higher during OpHrs compared with N-OpHrs, reflecting events such as train arrival/departure during OpHrs. Organic compounds were composed of aromatic hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) which are known to be harmful to health. Specific ratios of PAHs were identified for underground transport that may reflect an interaction between PAHs and fine particles. Scanning transmission electron microscopy (STEM) chemical maps of fine and ultrafine fractions show they are composed of Fe and O in the form of magnetite and nanosized mixtures of metals including Cr, Al, Ni and Mn. These findings, and the low air change rate (0.17 to 0.46 h-1), highlight the need to improve the ventilation conditions
Characteristics of fine and ultrafine aerosols in the London underground
\ua9 2022 The Authors. Underground railway systems are recognised spaces of increased personal pollution exposure. We studied the number-size distribution and physico-chemical characteristics of ultrafine (PM0.1), fine (PM0.1â2.5) and coarse (PM2.5â10) particles collected on a London underground platform. Particle number concentrations gradually increased throughout the day, with a maximum concentration between 18:00 h and 21:00 h (local time). There was a maximum decrease in mass for the PM2.5, PM2.5â10 and black carbon of 3.9, 4.5 and ~ 21-times, respectively, between operable (OpHrs) and non-operable (N-OpHrs) hours. Average PM10 (52 ÎŒg mâ3) and PM2.5 (34 ÎŒg mâ3) concentrations over the full data showed levels above the World Health Organization Air Quality Guidelines. Respiratory deposition doses of particle number and mass concentrations were calculated and found to be two- and four-times higher during OpHrs compared with N-OpHrs, reflecting events such as train arrival/departure during OpHrs. Organic compounds were composed of aromatic hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) which are known to be harmful to health. Specific ratios of PAHs were identified for underground transport that may reflect an interaction between PAHs and fine particles. Scanning transmission electron microscopy (STEM) chemical maps of fine and ultrafine fractions show they are composed of Fe and O in the form of magnetite and nanosized mixtures of metals including Cr, Al, Ni and Mn. These findings, and the low air change rate (0.17 to 0.46 hâ1), highlight the need to improve the ventilation conditions
Earliest Triassic microbialites in the South China Block and other areas; controls on their growth and distribution
Earliest Triassic microbialites (ETMs) and inorganic carbonate crystal fans formed after the end-Permian mass extinction (ca. 251.4 Ma) within the basal Triassic Hindeodus parvus conodont zone. ETMs are distinguished from rarer, and more regional, subsequent Triassic microbialites. Large differences in ETMs between northern and southern areas of the South China block suggest geographic provinces, and ETMs are most abundant throughout the equatorial Tethys Ocean with further geographic variation. ETMs occur in shallow-marine shelves in a superanoxic stratified ocean and form the only widespread Phanerozoic microbialites with structures similar to those of the Cambro-Ordovician, and briefly after the latest Ordovician, Late Silurian and Late Devonian extinctions. ETMs disappeared long before the mid-Triassic biotic recovery, but it is not clear why, if they are interpreted as disaster taxa. In general, ETM occurrence suggests that microbially mediated calcification occurred where upwelled carbonate-rich anoxic waters mixed with warm aerated surface waters, forming regional dysoxia, so that extreme carbonate supersaturation and dysoxic conditions were both required for their growth. Long-term oceanic and atmospheric changes may have contributed to a trigger for ETM formation. In equatorial western Pangea, the earliest microbialites are late Early Triassic, but it is possible that ETMs could exist in western Pangea, if well-preserved earliest Triassic facies are discovered in future work
Strategies for Investigating Early Mars Using Returned Samples
The 2011 Visions & Voyages Planeary Science Decadal Survey identified making significant progress toward the return of samples from Mars as the highest priority goal for flagship missions in next decade. Numerous scientific objectives have been identified that could be advanced through the potential return and analysis of martian rock, regolith, and atmospheric samples. The analysis of returned martian samples would be particularly valuable in in-creasing our understanding of Early Mars. There are many outstanding gaps in our knowledge about Early Mars in areas such as potential astrobiology, geochronology, planetary evolution (including the age, context, and processes of accretion, differentiation, magmatic, and magnetic history), the history of water at the martian surface, and the origin and evolution of the martian atmosphere. Here we will discuss scientific objectives that could be significantly advanced by Mars sample return
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