High Temperature Phase Transitions in Two-Scalar Theories with Large NN Techniques

We consider a theory of a scalar one-component field $\phi$ coupled to a scalar $N$-component field $\chi$. Using large $N$ techiques we calculate the effective potential in the leading order in $1/N$. We show that this is equivalent to a resummation of an infinite subclass of graphs in perturbation theory, which involve fluctuations of the $\chi$ field only. We study the temperature dependence of the expectation value of the $\phi$ field and the resulting first and second order phase transitions.Comment: 11 pages, LaTex, includes 5 uuencoded postscript figures, OUTP-94-11

Soil genesis and development, lesson 3: Soil forming factors

This lesson explores the five major factors of soil formation—(1) climate, (2) organisms, (3) time, (4) topography, and (5) parent material—and their influence in forming soil. The distinction between active and passive factors, moisture and temperature regimes, organism and topographic influences, and parent material sources are described. At the completion of this lesson, students will be able to do the following: 1. Identify the five factors of soil formation. 2. Explain the effects of each of the factors on soil formation. 3. Explain how types of parent material differ in terms of mode of deposition and degree of sorting. The lesson is written to target educational needs of lower-level undergraduate students and is available for use by the public and educational institutions

Soil genesis and development, lesson 2: Weathering processes of rocks and minerals

Weathering of rocks and minerals, which include physical, chemical, and biological processes, contributes to the development of soil. The degree of weathering depends not only on the rock and mineral composition but also on climate and biological activities. Experiential learning activities for different global regions support the learning objectives. At the completion of this lesson, students will be able to do the following: 1. Describe how climatic factors influence the weathering of rocks and minerals. 2. Define and distinguish physical, chemical, and biological weathering processes. The lesson is written to target educational needs of lower-level undergraduate students in earth and environmental sciences and is available for use by the public and educational institutions

Soil genesis and development, lesson 4: Soil profile development

The processes occurring over time in a soil are reflected in vertical and lateral physical and chemical characteristics of that soil. The four soil forming processes, in conjunction with the five factors of soil formation, organize parent material into a soil profile that consists of soil horizons. These processes can occur over millennia; however, they can also be influenced by short-term variables such as human use. Understanding the processes enables interpretation of the natural history of a soil and provides a starting point to evaluate how future changes will affect the soil resource. Combining landscape history with knowledge of principles of soil profile development allows for more precise and effective land use planning, from residential development to precision agricultural practices. At the completion of this lesson, students will be able to do the following: 1. Describe the four major soil forming processes. 2. Describe how these four processes redistribute soil materials in vertical and horizontal dimensions. 3. Explain which soil processes are dominant in each soil horizon. 4. Develop a profile horizon sequence based on given soil properties and a set of soil forming factors 5. Describe the general soil forming processes based on the soil forming factors that led to the development of a given soil profile. The lesson is written to target educational needs of lower-level undergraduate students and is open for use by the public and educational institutions

Soil genesis and development, lesson 5: Soil classification and geography

The system of soil classification developed by the United States Department of Agriculture (USDA) is called Soil Taxonomy. This lesson focuses on broad descriptions of soils at the Order level of classification. At the completion of this lesson, students will be able to do the following: 1. Describe the structure of the USDA soil taxonomic system. 2. Describe the defining characteristic(s) of each of the 12 soil Orders. 3. Apply the concept of soil forming factors to the formation and occurrence of each of the 12 soil Orders. 4. Identify regional scale occurrences of soil orders in the USA. The lesson is written to target educational needs of lowerlevel undergraduate students and is open for use by the public and educational institutions

Soil genesis and development, lesson 1: Rocks, minerals, and soils

Most soil parent materials were rocks at some time in their history. The minerals in rocks may contribute to soil fertility and other soil properties long after the original rock is gone. Consequently, it is a valuable skill to be able to identify broad categories of rock. This lesson will discuss igneous, metamorphic, and sedimentary rocks and the minerals found in them. The lesson will also provide opportunities for students to identify rocks based on given characteristics. At the completion of this lesson, students will be able to do the following: 1. Classify rocks based on visual characteristics according to the major types: igneous, metamorphic, and sedimentary. 2. Predict the influence of “parent” rock on soil properties. The lesson uses an interactive approach, embedding questions in each section of the lesson. The lesson is written to target educational needs of lower-level undergraduate students and is open for use by the public and educational institutions

Insights into the function of silver as an oxidation catalyst by ab initio, atomistic thermodynamics

To help understand the high activity of silver as an oxidation catalyst, e.g., for the oxidation of ethylene to epoxide and the dehydrogenation of methanol to formaldehyde, the interaction and stability of oxygen species at the Ag(111) surface has been studied for a wide range of coverages. Through calculation of the free energy, as obtained from density-functional theory and taking into account the temperature and pressure via the oxygen chemical potential, we obtain the phase diagram of O/Ag(111). Our results reveal that a thin surface-oxide structure is most stable for the temperature and pressure range of ethylene epoxidation and we propose it (and possibly other similar structures) contains the species actuating the catalysis. For higher temperatures, low coverages of chemisorbed oxygen are most stable, which could also play a role in oxidation reactions. For temperatures greater than about 775 K there are no stable oxygen species, except for the possibility of O atoms adsorbed at under-coordinated surface sites Our calculations rule out thicker oxide-like structures, as well as bulk dissolved oxygen and molecular ozone-like species, as playing a role in the oxidation reactions.Comment: 15 pages including 9 figures, Related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm

Sub-surface Oxygen and Surface Oxide Formation at Ag(111): A Density-functional Theory Investigation

To help provide insight into the remarkable catalytic behavior of the oxygen/silver system for heterogeneous oxidation reactions, purely sub-surface oxygen, and structures involving both on-surface and sub-surface oxygen, as well as oxide-like structures at the Ag(111) surface have been studied for a wide range of coverages and adsorption sites using density-functional theory. Adsorption on the surface in fcc sites is energetically favorable for low coverages, while for higher coverage a thin surface-oxide structure is energetically favorable. This structure has been proposed to correspond to the experimentally observed (4x4) phase. With increasing O concentrations, thicker oxide-like structures resembling compressed Ag2O(111) surfaces are energetically favored. Due to the relatively low thermal stability of these structures, and the very low sticking probability of O2 at Ag(111), their formation and observation may require the use of atomic oxygen (or ozone, O3) and low temperatures. We also investigate diffusion of O into the sub-surface region at low coverage (0.11 ML), and the effect of surface Ag vacancies in the adsorption of atomic oxygen and ozone-like species. The present studies, together with our earlier investigations of on-surface and surface-substitutional adsorption, provide a comprehensive picture of the behavior and chemical nature of the interaction of oxygen and Ag(111), as well as of the initial stages of oxide formation.Comment: 17 pages including 14 figures, Related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm

Perturbative Computation of the Gluonic Effective Action via Polyaokov's World-Line Path Integral

The Polyakov world-line path integral describing the propagation of gluon field quanta is constructed by employing the background gauge fixing method and is subsequently applied to analytically compute the divergent terms of the one (gluonic) loop effective action to fourth order in perturbation theory. The merits of the proposed approach is that, to a given order, it reduces to performing two integrations, one over a set of Grassmann and one over a set of Feynman-type parameters through which one manages to accomodate all Feynman diagrams entering the computation at once.Comment: 21 page

Biochemical profile, eating habits, and telomere length among Brazilian children and adolescents

Objectives: Lifestyle, obesity, and eating habits are emerging as determinants for the instability of telomeres. The increase in childhood and adolescent obesity and the association of biochemical profiles and dietary components with telomere length (TL) makes it an important issue in nutritional research. The aim of the present study was to investigate TL and its association with ethnic background, adiposity, clinical and biochemical parameters, and dietary patterns among Brazilian children and adolescents. Methods: A cross-sectional study encompassing 981 children and adolescents between 7 and 17 y of age was performed. Dietary intake habits, anthropometry, and clinical data were collected. TL analysis was performed by quantitative polymerase chain reaction. Results: Children presented significantly longer TL than adolescents (P = 0.046). Participants who self-declared as black, mulatto, or brown (P < 0.001) also showed longer TL than those who were white. Regarding biochemical parameters, individuals with altered glucose levels had shorter TL than normoglycemic participants in the total sample (P = 0.014). Such difference remained statistically significant in adolescents (P = 0.019). Participants who reported eating fruits and vegetables regularly had longer TL than those who did not (P < 0.001). Conclusion: The results suggested that both biochemical parameters and the intake of antioxidant-rich food, such as fruits and vegetables, are associated with the stability of telomere biology among young Brazilians