Polysomes of bovine anterior pituitary gland and their role in hormone and protein biosynthesis

This article does not have an abstract

Aridification of Central Asia and uplift of the Altai and Hangay mountains, Mongolia: stable isotope evidence

Central Asia has become increasingly arid during the Cenozoic, though the mechanisms behind this aridification remain unresolved. Much attention has focused on the influence and uplift history of the Tibetan Plateau. However, the role of ranges linked to India-Asia convergence but well north of the Plateau—including the Altai, Sayan, and Hangay—in creating the arid climate of Central Asia is poorly understood. Today, these ranges create a prominent rain shadow, effectively separating the boreal forest to the north from the deserts of Central Asia. To explore the role of these mountains in modifying climate since the late Eocene, we measured carbon and oxygen stable isotopes in paleosol carbonates from three basins along a 650 km long transect at the northern edge of the Gobi Desert in Mongolia and in the lee of the Altai and Hangay mountains. We combine these data with modern air-parcel back-trajectory modeling to understand regional moisture transport pathways at each basin. In all basins, δ¹³C increases, with the largest increase in western Mongolia. The first δ¹³C increase occurs in central and southwestern Mongolia in the Oligocene. δ¹³C again increases from the upper Miocene to the Quaternary in western and southwestern Mongolia. We use a 1-D soil diffusion model to demonstrate that these δ¹³C increases are linked to declines in soil respiration driven by dramatic increases in aridity. Using modern-day empirical relations between mean annual precipitation and soil respiration, we estimate that precipitation has likely more than halved over the Neogene. Given the importance of the Hangay and Altai in steering moisture in Mongolia, we attribute these changes to differential surface uplift of the Hangay and Altai. Surface uplift in the Hangay began by the early Oligocene, blocking Siberian moisture and aridifying the northern Gobi. In contrast, surface uplift of the Altai began in the late Miocene, blocking moisture from reaching western Mongolia. Thus, the northern Gobi became increasingly arid east to west since the late Eocene, likely driven by orographic development in the Hangay during the Oligocene and the Altai in the late Miocene through Pliocene

The impact of neogene grassland expansion and aridification on the isotopic composition of continental precipitation

The late Cenozoic was a time of global cooling, increased aridity, and expansion of grasslands. In the last two decades numerous records of oxygen isotopes have been collected to assess plant ecological changes, understand terrestrial paleoclimate, and to determine the surface history of mountain belts. The δ¹⁸(O) values of these records, in general, increase from the mid-Miocene to the Recent. We suggest that these records record an increase in aridity and expansion of grasslands in midlatitude continental regions. We use a nondimensional isotopic vapor transport model coupled with a soil water isotope model to evaluate the role of vapor recycling and transpiration by different plant functional types. This analysis shows that increased vapor recycling associated with grassland expansion along with biomechanistic changes in transpiration by grasses themselves conspires to lower the horizontal gradient in the δ¹⁸(O) of atmospheric vapor as an air mass moves into continental interiors. The resulting signal at a given inland site is an increase in δ¹⁸(O) of precipitation with the expansion of grasslands and increasing aridity, matching the general observed trend in terrestrial Cenozoic δ¹⁸(O) records. There are limits to the isotopic effect that are induced by vapor recycling, which we refer to here as a “hydrostat.” In the modern climate, this hydrostatic limit occurs at approximately the boundary between forest and grassland ecosystems

Seismology of the Sun : Inference of Thermal, Dynamic and Magnetic Field Structures of the Interior

Recent overwhelming evidences show that the sun strongly influences the Earth's climate and environment. Moreover existence of life on this Earth mainly depends upon the sun's energy. Hence, understanding of physics of the sun, especially the thermal, dynamic and magnetic field structures of its interior, is very important. Recently, from the ground and space based observations, it is discovered that sun oscillates near 5 min periodicity in millions of modes. This discovery heralded a new era in solar physics and a separate branch called helioseismology or seismology of the sun has started. Before the advent of helioseismology, sun's thermal structure of the interior was understood from the evolutionary solution of stellar structure equations that mimicked the present age, mass and radius of the sun. Whereas solution of MHD equations yielded internal dynamics and magnetic field structure of the sun's interior. In this presentation, I review the thermal, dynamic and magnetic field structures of the sun's interior as inferred by the helioseismology.Comment: To be published in the proceedings of the meeting "3rd International Conference on Current Developments in Atomic, Molecular, Optical and Nano Physics with Applications", December 14-16, 2011, New Delhi, Indi

Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory

Data from the Pierre Auger Observatory are analyzed to search for anisotropies near the direction of the Galactic Centre at EeV energies. The exposure of the surface array in this part of the sky is already significantly larger than that of the fore-runner experiments. Our results do not support previous findings of localized excesses in the AGASA and SUGAR data. We set an upper bound on a point-like flux of cosmic rays arriving from the Galactic Centre which excludes several scenarios predicting sources of EeV neutrons from Sagittarius $A$. Also the events detected simultaneously by the surface and fluorescence detectors (the `hybrid' data set), which have better pointing accuracy but are less numerous than those of the surface array alone, do not show any significant localized excess from this direction.Comment: Matches published versio

Measurement of the Depth of Maximum of Extensive Air Showers above 10^18 eV

We describe the measurement of the depth of maximum, Xmax, of the longitudinal development of air showers induced by cosmic rays. Almost four thousand events above 10^18 eV observed by the fluorescence detector of the Pierre Auger Observatory in coincidence with at least one surface detector station are selected for the analysis. The average shower maximum was found to evolve with energy at a rate of (106 +35/-21) g/cm^2/decade below 10^(18.24 +/- 0.05) eV and (24 +/- 3) g/cm^2/decade above this energy. The measured shower-to-shower fluctuations decrease from about 55 to 26 g/cm^2. The interpretation of these results in terms of the cosmic ray mass composition is briefly discussed.Comment: Accepted for publication by PR

Operations of and Future Plans for the Pierre Auger Observatory

Technical reports on operations and features of the Pierre Auger Observatory, including ongoing and planned enhancements and the status of the future northern hemisphere portion of the Observatory. Contributions to the 31st International Cosmic Ray Conference, Lodz, Poland, July 2009.Comment: Contributions to the 31st ICRC, Lodz, Poland, July 200

The exposure of the hybrid detector of the Pierre Auger Observatory

The Pierre Auger Observatory is a detector for ultra-high energy cosmic rays. It consists of a surface array to measure secondary particles at ground level and a fluorescence detector to measure the development of air showers in the atmosphere above the array. The "hybrid" detection mode combines the information from the two subsystems. We describe the determination of the hybrid exposure for events observed by the fluorescence telescopes in coincidence with at least one water-Cherenkov detector of the surface array. A detailed knowledge of the time dependence of the detection operations is crucial for an accurate evaluation of the exposure. We discuss the relevance of monitoring data collected during operations, such as the status of the fluorescence detector, background light and atmospheric conditions, that are used in both simulation and reconstruction.Comment: Paper accepted by Astroparticle Physic