Meteorological satellites

An overview is presented of the meteorological satellite programs that have been evolving from 1958 to the present, and plans for the future meteorological and environmental satellite systems that are scheduled to be placed into service in the early 1980's are reviewed. The development of the TIROS family of weather satellites, including TIROS, ESSA, ITOS/NOAA, and the present TIROS-N (the third generation operational system) is summarized. The contribution of the Nimbus and ATS technology satellites to the development of the operational-orbiting and geostationary satellites is discussed. Included are descriptions of both the TIROS-N and the DMSP payloads currently under development to assure a continued and orderly growth of these systems into the 1980's

Ecosystem shifts at two Mid-Holocene tipping points in the alpine Lake Son Kol (Kyrgyzstan, Central Asia)

Tipping points can be defined as critical ecosystem thresholds that start self-enforced dynamics pushing systems into new stable states. Many lake ecosystems of arid Central Asia are sensitive to hydrological changes as they are located at the intersection of the influence of the dry Siberian Anticyclone and the relatively humid mid-latitude Westerlies, and their sediment records can be used to study past tipping points. We studied subfossil chironomid remains preserved in a ca. 6000-year-long sediment record from the Central Asian lake Son Kol (Central Kyrgyzstan) to reconstruct past ecosystem dynamics. Our results show abrupt transitions from a chironomid fauna dominated by macrophyte-associated, salinity-indicating taxa, to a vegetation-independent fauna, and subsequently to a macrophyte-associated, freshwater-indicating fauna. A comparison of the chironomid-based environmental reconstruction to other proxy indicators from the same record suggests a phase of increased Westerly strength starting about 4900 cal. yr BP. This increase led to enhanced precipitation and sediment fluxes into the lake, which in turn led to high turbidity levels and consequently to a macrophyte collapse causing abrupt changes in the chironomid fauna. At 4300 cal. yr BP, a weakening of the Westerlies in combination with higher lake levels led to lower turbidity and ultimately to the recovery of the macrophyte population and associated changes in the chironomid assemblage. These two sequences of events show how the occurrence of a gradual change in an external trigger (Westerlies) can trigger a cascade of within-lake processes (turbidity, macrophyte density) and may ultimately lead to an abrupt reorganisation of the ecosystem (chironomid fauna), providing models for tipping points

Topological Reverberations in Flat Space-times

We study the role played by multiply-connectedness in the time evolution of the energy E(t) of a radiating system that lies in static flat space-time manifolds M_4 whose t=const spacelike sections M_3 are compact in at least one spatial direction. The radiation reaction equation of the radiating source is derived for the case where M_3 has any non-trivial flat topology, and an exact solution is obtained. We also show that when the spacelike sections are multiply-connected flat 3-manifolds the energy E(t) exhibits a reverberation pattern with discontinuities in the derivative of E(t) and a set of relative minima and maxima, followed by a growth of E(t). It emerges from this result that the compactness in at least one spatial direction of Minkowski space-time is sufficient to induce this type of topological reverberation, making clear that our radiating system is topologically fragile. An explicit solution of the radiation reaction equation for the case where M_3 = R^2 x S^1 is discussed, and graphs which reveal how the energy varies with the time are presented and analyzed.Comment: 16 pages, 4 figures, REVTEX; Added five references and inserted clarifying details. Version to appear in Int. J. Mod. Phys. A (2000

Limnogeologúa de Laguna Chungará y cambio climático durante el Holoceno superior en el altiplano chileno septentrional

[Resumen] El estudio sísmico de la Laguna Chungará (69° 30' O, 18° 15'S, 4520 m. s.n.m, Altiplano chileno septentrional) y el análisis sedimentológico de varios sondeos ha permitido reconstruir la evolución de la sedimentación lacustre en el lago durante el Holoceno Superior. Se han identificado dos asociaciones de facies: i) litoral, más somera, compuesta por facies de turbera y in plataforma lacustre, más profunda, compuesta por facies con abundantes fragmentos de Characeae. Estas facies alternan en tres ciclos sedimentarios provocados por fluctuaciones en el nivel del lago. Estas variaciones hidrológicas en la laguna han sido causadas por cambios en el balance hídrico que a su vez reflejan importantes fluctuaciones climáticas durante el Holoceno Superior.[Abstract] We reconstruct the Late Holocene sedimentary history of Laguna Chungará (69° 30' W, 18° 10'5, 4520 m.a.s.l., northern Chilean Altiplano) based on high resolution seismic profiling and sedimentologic analyses of cores. Two sedimentary facies associations have been defined and interpreted: n macrophytedominant littoral, composed of black muds with macrophyte remains and peaty muds, and in Characeae-dominant lacustrine self, composed of gray muds and sands with abundant Characeae remains. The two facies associations define three cycles caused by oscillations in the lake level from shallower (macrophyte) to deeper (Characeae) conditions. Changes in the hydrology of Laguna Chungará reflect variations in the effective moisture (precipitation - evaporation) in the Altiplano during the Late Holocene

Transcription activation depends on the length of the RNA polymerase II C‐terminal domain

Eukaryotic RNA polymerase II (Pol II) contains a tail‐like, intrinsically disordered carboxy‐terminal domain (CTD) comprised of heptad‐repeats, that functions in coordination of the transcription cycle and in coupling transcription to co‐transcriptional processes. The CTD repeat number varies between species and generally increases with genome size, but the reasons for this are unclear. Here, we show that shortening the CTD in human cells to half of its length does not generally change pre‐mRNA synthesis or processing in cells. However, CTD shortening decreases the duration of promoter‐proximal Pol II pausing, alters transcription of putative enhancer elements, and delays transcription activation after stimulation of the MAP kinase pathway. We suggest that a long CTD is required for efficient enhancer‐dependent recruitment of Pol II to target genes for their rapid activation

Charged pions from Ni on Ni collisions between 1 and 2 AGeV

Charged pions from Ni + Ni reactions at 1.05, 1.45 and 1.93 AGeV are measured with the FOPI detector. The mean $\pi^{\pm}$ multiplicities per mean number of participants increase with beam energy, in accordance with earlier studies of the Ar + KCl and La + La systems. The pion kinetic energy spectra have concave shape and are fitted by the superposition of two Boltzmann distributions with different temperatures. These apparent temperatures depend only weakly on bombarding energy. The pion angular distributions show a forward/backward enhancement at all energies, but not the $\Theta = 90^0$ enhancement which was observed in case of the Au + Au system. These features also determine the rapidity distributions which are therefore in disagreement with the hypothesis of one thermal source. The importance of the Coulomb interaction and of the pion rescattering by spectator matter in producing these phenomena is discussed.Comment: 22 pages, Latex using documentstyle[12pt,a4,epsfig], to appear in Z. Phys.