Gas adsorption/desorption in silica aerogels: a theoretical study of scattering properties

We present a numerical study of the structural correlations associated to gas adsorption/desorption in silica aerogels in order to provide a theoretical interpretation of scattering experiments. Following our earlier work, we use a coarse-grained lattice-gas description and determine the nonequilibrium behavior of the adsorbed gas within a local mean-field analysis. We focus on the differences between the adsorption and desorption mechanisms and their signature in the fluid-fluid and gel-fluid structure factors as a function of temperature. At low temperature, but still in the regime where the isotherms are continuous, we find that the adsorbed fluid density, during both filling and draining, is correlated over distances that may be much larger than the gel correlation length. In particular, extended fractal correlations may occur during desorption, indicating the existence of a ramified cluster of vapor filled cavities. This also induces an important increase of the scattering intensity at small wave vectors. The similarity and differences with the scattering of fluids in other porous solids such as Vycor are discussed.Comment: 16 pages, 15 figure

Vegetable Lecithin as an Antioxidant

Vegetable lecithins have been recommended for use as antioxygenic or stabilizing substances to delay rancidity in fats and oils, although complete experimental evidence as to their efficacy is lacking. Measuring the induction period of the oxidation of lard by means of the oven-test, two commercial samples of soy-bean lecithin were shown to be weak antioxidants, having indices of 1.7 and 1.8 respectively

Adsorption in non interconnected pores open at one or at both ends: A reconsideration of the origin of the hysteresis phenomenon

We report on an experimental study of adsorption isotherme of nitrogen onto porous silicon with non interconnected pores open at one or at both ends in order to check for the first time the old (1938) but always current idea based on Cohan's description which suggests that the adsorption of gaz should occur reversibly in the first case and irreversibly in the second one. Hysteresis loops, the shape of which is usually associated to interconnections in porous media, are observed whether the pores are open at one or at both ends in contradiction with Cohan's model.Comment: 5 pages, 4 EPS figure

Capillary condensation in disordered porous materials: hysteresis versus equilibrium behavior

We study the interplay between hysteresis and equilibrium behavior in capillary condensation of fluids in mesoporous disordered materials via a mean-field density functional theory of a disordered lattice-gas model. The approach reproduces all major features observed experimentally. We show that the simple van der Waals picture of metastability fails due to the appearance of a complex free-energy landscape with a large number of metastable states. In particular, hysteresis can occur both with and without an underlying equilibrium transition, thermodynamic consistency is not satisfied along the hysteresis loop, and out-of-equilibrium phase transitions are possible.Comment: 4 pages, 4 figure

FAPRI 2000 U.S. Agricultural Outlook

Crop Production/Industries, Livestock Production/Industries,

Profiling a decade of information systems frontiers’ research

This article analyses the first ten years of research published in the Information Systems Frontiers (ISF) from 1999 to 2008. The analysis of the published material includes examining variables such as most productive authors, citation analysis, universities associated with the most publications, geographic diversity, authors’ backgrounds and research methods. The keyword analysis suggests that ISF research has evolved from establishing concepts and domain of information systems (IS), technology and management to contemporary issues such as outsourcing, web services and security. The analysis presented in this paper has identified intellectually significant studies that have contributed to the development and accumulation of intellectual wealth of ISF. The analysis has also identified authors published in other journals whose work largely shaped and guided the researchers published in ISF. This research has implications for researchers, journal editors, and research institutions

FAPRI 2000 World Agricultural Outlook

The Food and Agricultural Policy Research Institute (FAPRI) prepares a preliminary agricultural outlook on world agricultural production, consumption, and trade every fall. This is followed by an outside review, re-evaluation of projections, and completion of the final baseline in January. The FAPRI 2000 World Agricultural Outlook presents these final projections for world agricultural markets. A companion volume, the FAPRI 2000 U.S. Agricultural Outlook, presents the U.S. component of the baseline. FAPRI projections assume average weather patterns worldwide, existing policy, and policy commitments under current trade agreements. FAPRI projections do not include conjectures on potential policy changes, such as those resulting from the likely eastward enlargement of the European Union (EU). The baseline predicts recovery of world agricultural production, consumption, and trade, but with remaining price weakness for crops. Stock-to-use ratios in world crop markets remain high despite the strong recovery of Asian and Latin American economies. Above-average yields kept world production high relative to demand in 1999. In contrast, pork and beef prices are increasing significantly above their 1999 level. The physical volume of U.S. agricultural exports is projected to reverse the downward trend of fiscal year (FY) 1999, whereas the value of agricultural exports continue to decline for one more year before recovering because of low crop prices in 2000/01. World crop trade is projected to increase by 55 million metric tons (mmt) in the coming decade, with the United States capturing 49 percent of the expanded market, but still unable to increase its market share by a large percentage. Following this expansion of the market, grain prices increase by 35 percent in the projection period, but still stay well below the peak of 1995/96. The increase in world crop trade reflects the increasing specialization occurring in world agriculture. Increased market access and land scarcity in many Asian economies induce them to import grains and oilseeds to meet their feed demand. Developing Asia remains the fastest growing market for corn in the next decade. With implementation of Agenda 2000 reforms, the EU will reduce its wheat domestic price relative to the world price and will export wheat without subsidies after 2004, constraining gains in market shares for the United States. EU barley exports will expand significantly in the coming years but are likely to be constrained by General Agreement on Tariffs and Trade (GATT) commitments on export subsidies after 2004. World meat trade will increase by 31 percent over the next decade. The United States has become a competitive producer and exporter of meat products. In the coming decade, the United States will experience the largest meat export growth rates among major exporters of beef, pork, and broilers. U.S. exporters capture more than 70 percent of the growth in trade, increasing their share of the combined meat markets from 23 percent in 1999 to 37 percent in 2009. Meat imports are recovering and expanding rapidly in Japan, South Korea, and Taiwan. In Japan, the share of imports in consumption increases from 38 percent in the 1990s to 49 percent at the end of the next decade. Taiwan meat imports will triple from 1990-1999 levels to 2000-2009 levels, driven by imports of beef, non muscle pork products, and the opening of the poultry market. Recovery of Asian food demand will prompt dairy prices to grow by about 1 percent per year over the next decade. Total milk production is projected to increase, with particularly strong growth in the United States, Mexico, Argentina, and Brazil. Most of the growth occurs through yield increases. Per capita cheese consumption is expected to grow by 1 to 2 percent a year in most countries.Crop Production/Industries, Livestock Production/Industries,

A Survey of z>5.7 Quasars in the Sloan Digital Sky Survey II: Discovery of Three Additional Quasars at z>6

We present the discovery of three new quasars at z>6 in 1300 deg^2 of SDSS imaging data, J114816.64+525150.3 (z=6.43), J104845.05+463718.3 (z=6.23) and J163033.90+401209.6 (z=6.05). The first two objects have weak Ly alpha emission lines; their redshifts are determined from the positions of the Lyman break. They are only accurate to 0.05 and could be affected by the presence of broad absorption line systems. The last object has a Ly alpha strength more typical of lower redshift quasars. Based on a sample of six quasars at z>5.7 that cover 2870 deg^2 presented in this paper and in Paper I, we estimate the comoving density of luminous quasars at z 6 and M_{1450} < -26.8 to be (8 +/- 3)x10^{-10} Mpc^{-3} (for H_0 = 50 km/s/Mpc, Omega = 1). HST imaging of two z>5.7 quasars and high-resolution ground-based images (seeing 0.4'') of three additional z>5.7 quasars show that none of them is gravitationally lensed. The luminosity distribution of the high-redshfit quasar sample suggests the bright end slope of the quasar luminosity function at z 6 is shallower than Psi L^{-3.5} (2-sigma), consistent with the absence of strongly lensed objects.Comment: AJ in press (Apr 2003), 26 pages, 9 figure