Signal-to-noise enhancement in ground-based intensity observations of solarp modes

Intensity observations of solarp modes are needed to form a complete picture of wave propagation in the photosphere. Ground-based intensity observations are severely hampered by terrestrial atmospheric noise. Partial cancellation of the noise power can be achieved if two spectra having disparate signal-to-noise ratios, and based on time series acquired simultaneously at the same site, are combined. A method of combining the spectra is suggested in which one amplitude is scaled and subtracted from the other. The result is squared yielding a positive-definite power density. To test the method, the intensity of light scattered by the Earths atmosphere was recorded at fifteen-second intervals in two narrow bands centered on 0.5 and 1.6. When the two resulting spectra were combined, the noise power was attenuated by a factor of 2.7. The scale factor was varied about its optimum value, revealing that noise peaks have a different signature than signal peaks, and opening up the possibility of a new tool in discrimination against noise peaks. Maxima at symmetry-allowed frequencies and minima at symmetry-forbidden frequencies indicate that the probability that these results are obtained by chance is only 6.1 × 10^–4. The positions of these maxima and minima also support the solar-cycle dependent frequency shifts found by Pallé, Régulo, and Roca Cortés (1990a).     

Petrology and geochemistry of the Northwest Africa 3368 eucrite

Abstract– Analysis of the mineralogy, isotopic, and bulk compositions of the eucrite meteorites is imperative for understanding their origin on the asteroid 4 Vesta, the proposed parent body of the HED meteorites. We present here the petrology, mineral compositions, and bulk chemistry of several lithic components of the new brecciated basaltic eucrite Northwest Africa (NWA) 3368 to determine if all the lithologies reflect formation from one rock type or many rock types. The meteorite has three main lithologies: coarse‐ and fine‐grained clasts surrounded by a fine‐grained recrystallized silicate matrix. Silicate compositions are homogeneous, and the average rare earth element pattern for NWA 3368 is approximately 10× CI chondrites with a slight negative Eu anomaly. Major and trace element data place NWA 3368 with the Main Group‐Nuevo Laredo trend. High‐Ti chromites with ilmenite exsolution lamellae provide evidence of NWA 3368’s history of intense metamorphism. We suggest that this meteorite underwent several episodes of brecciation and metamorphism, similar to that proposed by Metzler et al. (1995) . We conclude that NWA 3368 is a monomict basaltic eucrite breccia related to known eucrites in texture and in mineral, bulk, and oxygen isotopic composition.     

The equity aspects of carbon dioxide-induced climate change

There is a growing scientific consensus that additional carbon dioxide being added to the earth's atmosphere (primarily as a result of fossil fuel combustion and deforestation) will eventually result in an alteration of global climates. While much uncertainty remains regarding the timing, nature and magnitude of such climatic changes, another controversy surrounds the issue of what, if anything, should be done either to avert such changes or to prepare for them. Some studies advocate a reduction of fossil fuel use, and a reversal of present deforestation trends in order to prevent climate changes from occurring. Other studies advocate prediction and adaptation as the preferred course of action. The present paper falls into this latter category, but attempts to examine a number of fundamental obstacles which will prevent fossil fuel use reductions or changes in deforestation activities. An understanding of these moral and ethical issues is crucial for approaching not only the specific question of global climate change, but also the general class of environmental problems that will require international co-operation to resolve.     

A method to measure the isotopic (C) composition of dissolved organic carbon using a high temperature combustion instrument

The stable isotopes of dissolved organic carbon (DOC) are a powerful tool for distinguishing sources and inputs of organic matter in aquatic systems. While several methods exist to perform these analyses, no labs routinely utilize a high temperature combustion (HTC) instrument. Advantages of HTC instruments include rapid analysis, small sample volumes and minimal sample preparation, making them the favored devices for most routine oceanic DOC concentration measurements. We developed a stable carbon DOC method based around an HTC system. This method has the benefit of a simple setup, requiring neither vacuum nor high pressures. The main drawback of the method is a significant blank, requiring careful accounting of all blank sources for accurate isotopic and concentration values. We present here a series of experiments to determine the magnitude, source and isotopic composition of the HTC blank. Over time, the blank is very stable at  20 ng of carbon with a δ¹³C of − 18.1‰ vs. VPDB. The similarity of the isotopic composition of the blank and seawater samples makes corrections relatively minor. The precision of the method was determined by oxidizing organic standards with a wide isotopic and concentration range (− 9‰ to − 39‰; 18 μM to 124 μM). Analysis of seawater samples demonstrates the accuracy for low concentration, high salinity samples. The overall error on the measurement is approximately ± 0.8‰.