Short-period intensity oscillations in the solar corona observed during the total solar eclipse of 26 february 1998

Encouraged by the detection of high-frequency, low-amplitude continuum intensity oscillations in the solar corona during the total solar eclipse of 1995, we designed and fabricated a six-channel photometer incorporating low-noise Hamamatsu R647 photomultipliers. Fast photometry at five different locations in the solar corona was performed at Don Bosco Mission, Venezuela during the total solar eclipse of 26 February 1998. Three interference filters with passbands of about 150Å and centered around 4700, 4900, and 5000Å were used. The photometric data were recorded at a rate of 20 Hz in three channels and 50 Hz in the remaining three channels. The power spectrum analysis of one of the channels that recorded appreciable counts indicates the existence of intensity oscillations in the frequency range 0.01-0.2 Hz. A least-squares analysis yields 90.1, 25.2, and 6.9 s periods for the three prominent components which have amplitudes in the range 0.5-3.5% of the coronal brightness. These periods and their amplitudes are similar to those detected in the coronal intensity oscillations during the 1995 eclipse

Constraints on grain formation around carbon stars from laboratory studies of presolar graphite

We report the results of an investigation into the physical conditions in the mass outflows of asymptotic giant branch (AGB) carbon stars that are required for the formation of micron-sized presolar graphite grains, with and without previously formed internal crystals of titanium carbide (TiC). A lower mass limit of 1.1 M⊙ for stars capable of contributing grains to the solar nebula is derived. This mass limit, in conjunction with a mass-luminosity relation for carbon stars, identifies the region of the H-R diagram relevant to the production of presolar graphite. Detailed dynamical models of AGB outflows, along with constraints provided by kinetics and equilibrium thermodynamics, indicate that grain formation occurs at radii from 2.3 to 3.7 AU for AGB carbon stars in the 1.1-5 M⊙ range. This analysis also yields time intervals available for graphite growth that are on the order of a few years. By considering the luminosity variations of carbon stars, we show that grains formed during minima in the luminosity are likely to be evaporated subsequently, while those formed at luminosity maxima will survive. We calculate strict upper limits on grain sizes for graphite and TiC in spherically symmetric AGB outflows. Graphite grains can reach diameters in the observed micron size range (1-2 µm) only under ideal growth conditions (perfect sticking efficiency, no evaporation, no depletion of gas species contributing to grain growth), and then only in outflows from carbon stars with masses ≲ 2.5 M⊙. The same is true for TiC grains that are found within presolar graphite, which have mean diameters of 24 ± 14 nm. In general, the mass-loss rates that would be required to produce the observed grain sizes in spherically symmetric outflows are at least an order of magnitude larger than the maximum observed AGB carbon star mass-loss rates. These results, as well as pressure constraints derived from equilibrium thermodynamics, force us to conclude that presolar graphite and TiC must form in regions of enhanced density (clumps, jets) in AGB outflows having small angular scales. As shown in the companion paper by Croat et al., the enrichment of 12C in many AGB graphites, and the overabundances of the s-process elements Mo, Zr, and Ru in the carbides found within them, often greatly exceed the values observed astronomically in AGB outflows. These observations not only lend further support to the idea that the outflows are clumpy, but also imply that the outflowing matter is not well mixed in the circumstellar envelope out to the radii where grain condensation takes place

A simple method of estimating folic acid absorption (a modified faecal excretion method)

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INVESTIGATION OF ADAPTIVE BEAMFORMING ALGORITHMS FOR COGNITIVE RADIO ARCHITECTURE

ABSTRACT The present fixed spectrum assignment policy becomes a bottleneck for more efficient spectrum utilization, as majority of the already scarce spectrum goes under-utilized. The concept of Cognitive Radio has been receiving increasing attention as a solution to the aforementioned quandary, since it equips the capability to optimally adapt their operating parameters according to the interactions with the surrounding radio environment. In this paper, the feasibility of a smart antenna to this system is analyzed and the performance of the different beamforming algorithms is compared

A successfully thrombolysed acute inferior myocardial infarction due to type A aortic dissection with lethal consequences: the importance of early cardiac echocardiography

Thrombolysis, a standard therapy for ST elevation myocardial infarction (STEMI) in non-PCI-capable hospitals, may be catastrophic for patients with aortic dissection leading to further expansion, rupture and uncontrolled bleeding. Stanford type A aortic dissection, rarely may mimic myocardial infarction. We report a case of a patient with an inferior STEMI thrombolysed with tenecteplase and followed by clinical and electrocardiographic evidence of successful reperfusion, which was found later to be a lethal acute aortic dissection. Prognostic implications of early diagnosis applying transthoracic echocardiography (TTE) are described

Failure or success? Defensive strategies and piecemeal change among racial inequalities in the Brazilian banking sector

We analyze how Brazilian Black Movement organizations and banks deployed different mechanisms like cooperation, cooptation, and confrontation that generated affirmative action initiatives in the banking sector at the beginning of this century. Black movement organizations triggered an institutional change by connecting fields and exploring a constellation of strategies. However, Brazilian banks adopted defensive strategies aiming to accommodate their interests. We find that only piecemeal change occurred, as the field’s structures – resource distribution and power – remained unscratched. We conclude by noting how the success of social movement strategies can depend upon the framing and sense-giving work that social movements conduct in their continuous jockeying activity toward incumbents