Neon Lights Up a Controversy: the Solar Ne/O Abundance

The standard solar model was so reliable that it could predict the existence of the massive neutrino. Helioseismology measurements were so precise that they could determine the depth of the convection zone. This agreement between theory and observation was the envy of all astrophysics -- until recently when sophisticated three-dimensional hydrodynamic calculations of the solar atmosphere reduced the metal content by a factor of almost two. Antia & Basu (2005) suggested that a higher value of the solar neon abundance, Ne/O = 0.52, would resolve this controversy. Drake & Testa (2005) presented strong evidence in favor of this idea from a sample of 21 Chandra stars with enhanced values of the neon abundance, Ne/O = 0.41. In this paper, we have analyzed solar active region spectra from the archive of the Flat Crystal Spectrometer on Solar Maximum Mission, a NASA mission from the 1980s, as well as full-Sun spectra from the pioneering days of X-ray astronomy in the 1960s. These data seem consistent with the standard neon-to-oxygen abundance value, Ne/O = 0.15 (Grevesse & Sauval 1998). If these results prove to be correct, than the enhanced-neon hypothesis will not resolve the current controversy.Comment: submitted to ApJ Letter

All Coronal Loops are the Same: Evidence to the Contrary

The 1998 April 20 spectral line data from the Coronal Diagnostics Spectrometer (CDS) on the {\it Solar and Heliospheric Observatory} (\SOHO) shows a coronal loop on the solar limb. Our original analysis of these data showed that the plasma was multi-thermal, both along the length of the loop and along the line of sight. However, more recent results by other authors indicate that background subtraction might change these conclusions, so we consider the effect of background subtraction on our analysis. We show Emission Measure (EM) Loci plots of three representative pixels: loop apex, upper leg, and lower leg. Comparisons of the original and background-subtracted intensities show that the EM Loci are more tightly clustered after background subtraction, but that the plasma is still not well represented by an isothermal model. Our results taken together with those of other authors indicate that a variety of temperature structures may be present within loops.Comment: Accepted for publication in ApJ Letter

Effects of NaCl on growth and activity of enzymes involved in carbon metabolism in leaves of tobacco (Nicotiana rustica)

The adverse effects of salt should not be the same in tobacco plants exposed to a permanent and transient high concentration of NaCl in its environment. Experiments were conducted in order to verify the hypothesis of reversibility of NaCl effects. The study of this reversibility is checked by monitoring a number of parameters in pre-stressed plants and then, replaced in normal conditions. Plants previously grown for 30 days on basic medium were treated for 7 days with 200 mM NaCl and then placed back on the basic culture without NaCl for 10 days. The results show that NaCl suppression leads to a resumption of growth with a decrease in the concentration of sodium (Na+) and chloride ions (Cl-). Hence, potassium content (K+) increases gradually in the leaves to reach the level obtained with unstressed plants. At the same time, there is a stimulation of the activities of phosphoenolpyruvate carboxylase (PEPC), malate dehydrogenase isoenzymes (NAD, NADP, NADH and NADPH-MDH) and isocitrate dehydrogenase (ICDH) after NaCl had been removed. Along with the boosting of the activity of these enzymes involved in the process of carbon assimilation, there is a gradual decrease in soluble sugars content, suggesting a resumption of the normal activity of photosynthetic assimilation process. All these results verify our hypothesis and can be explained by the ability of the plant to dilute the effects of Na+ and Cl- during the recovering period. An important result of this study is that a transient salinity is not necessarily followed by a significant depreciation in product yield or quality.Keywords: Tobacco, NaCl, reversibility, phosphoenolpyruvate carboxylase (PEPC), malate dehydrogenase (MDH), isocitrate dehydrogenase (ICDH

An experimental method of measuring the quasi-static and dynamic confined behaviour of PMMA

A testing device is presented for the experimental study of the confined behaviour of PMMA in compression under quasi-static loading or at high strain-rates. The constitutive relation of the material ring (allowing to confine the PMMA) being known, transverse gauges glued on its lateral surface allow for the measurement of the lateral confining pressure. The hydrostatic pressure and the Mises stress may be computed. Quasi-static and dynamic tests performed in a strain-rate range of 1e-3/s 1e3/s are processed with the method and compared to results of unconfined compression tests. It is found that the compressive behaviour of PMMA is weakly influenced by the level of pressure and much more sensitive to strain-rate: an elastic brittle behaviour is observed at high strain-rates in unconfined or confined conditions whereas elastoplastic behaviour is noted under quasi-static loading

Are Coronal Loops Isothermal or Multithermal? Yes!

Surprisingly few solar coronal loops have been observed simultaneously with TRACE and SOHO/CDS, and even fewer analyses of these loops have been conducted and published. The SOHO Joint Observing Program 146 was designed in part to provide the simultaneous observations required for in-depth temperature analysis of active region loops and determine whether these loops are isothermal or multithermal. The data analyzed in this paper were taken on 2003 January 17 of AR 10250. We used TRACE filter ratios, emission measure loci, and two methods of differential emission measure analysis to examine the temperature structure of three different loops. TRACE and CDS observations agree that Loop 1 is isothermal with Log T $=$ 5.85, both along the line of sight as well as along the length of the loop leg that is visible in the CDS field of view. Loop 2 is hotter than Loop 1. It is multithermal along the line of sight, with significant emission between 6.2 $<$ Log T $<$ 6.4, but the loop apex region is out of the CDS field of view so it is not possible to determine the temperature distribution as a function of loop height. Loop 3 also appears to be multithermal, but a blended loop that is just barely resolved with CDS may be adding cool emission to the Loop 3 intensities and complicating our results. So, are coronal loops isothermal or multithermal? The answer appears to be yes

Contribution of grazing areas to small ruminant production systems in the Mediterranean countries

Publishe

Web Mining for Web Personalization

Web personalization is the process of customizing a Web site to the needs of specific users, taking advantage of the knowledge acquired from the analysis of the user\u27s navigational behavior (usage data) in correlation with other information collected in the Web context, namely, structure, content, and user profile data. Due to the explosive growth of the Web, the domain of Web personalization has gained great momentum both in the research and commercial areas. In this article we present a survey of the use of Web mining for Web personalization. More specifically, we introduce the modules that comprise a Web personalization system, emphasizing the Web usage mining module. A review of the most common methods that are used as well as technical issues that occur is given, along with a brief overview of the most popular tools and applications available from software vendors. Moreover, the most important research initiatives in the Web usage mining and personalization areas are presented