Energy shifts in photoemission lines during the tetragonal- to cubic-phase transition in BaTiO3 single crystals and systems with CoFe2O4 and NiFe2O4 overlayers

In BaTiO₃ the phase transition from tetragonal to cubic is connected with the disappearance of the ferroelectric polarization. In photoelectron spectroscopy huge transient shifts in the binding energies of all core-level photoemission lines have been observed while heating and cooling through the Curie temperature. Excitation energies from 2 keV to 6 keV have been used to show this to be a bulk effect and not a surface effect alone. These observations are discussed in terms of charging, which results from the disappearance of the ferroelectric polarization. This mechanism has previously been proposed as the origin of electron emission in ferroelectric materials. Besides the jump-like shifts, additional permanent shifts in binding energies have been observed for the tetragonal and the cubic phase. These experimental shifts have been related to theoretical ones from ab initio calculations. In addition to BaTiO₃ single crystals, systems with CoFe₂O₄ and NiFe₂O₄ overlayers on BaTiO₃ have been investigated. The low conductivity of these layers sets them apart from metallic overlayers like Fe or Co, where the shifts are suppressed. This difference adds further support for charging as the origin of the effect.

Polyunsaturated fatty acids in the food chain in the United States

In the United States, intake of n-3 fatty acids is approximately 1.6 g/d ( approximately 0.7% of energy), of which 1.4 g is alpha-linolenic acid (ALA; 18:3) and 0.1-0.2 g is eicosapentaenoic acid (EPA; 20:5) and docosahexaenoic acid (DHA; 22:6). The primary sources of ALA are vegetable oils, principally soybean and canola. The predominant sources of EPA and DHA are fish and fish oils. Intake data indicate that the ratio of n-6 to n-3 fatty acids is approximately 9.8:1. Food disappearance data between 1985 and 1994 indicate that the ratio of n-6 to n-3 fatty acids has decreased from 12.4:1 to 10.6:1. This reflects a change in the profile of vegetable oils consumed and, in particular, an approximate 5.5-fold increase in canola oil use. The ratio of n-6 to n-3 fatty acids is still much higher than that recommended (ie, 2.3:1). Lower ratios increase endogenous conversion of ALA to EPA and DHA. Attaining the proposed recommended combined EPA and DHA intake of 0.65 g/d will require an approximately 4-fold increase in fish consumption in the United States. Alternative strategies, such as food enrichment and the use of biotechnology to manipulate the EPA and DHA as well as ALA contents of the food supply, will become increasingly important in increasing n-3 fatty acid intake in the US population.

Immunologic effects of marine- and plant-derived n-3 polyunsaturated fatty acids in nonhuman primates

The effect of marine- and plant-derived n-3 polyunsaturated fatty acids (PUFAs) on T cell-mediated immune response was studied in cynomolgus monkeys. Animals were first fed a 14-wk baseline diet; 10 animals were then fed diets containing 1.3% or 3.3% of energy as eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) which the other 10 were fed diets containing 3.5% or 5.3% of energy as alpha-linolenic acid (ALA) for two consecutive 14-wk periods. Both diets significantly decreased the percentage of T cells (except 1.3% EPA + DHA), T helper cells (except 1.3% EPA + DHA and 3.5% ALA), and T suppressor cells. Proliferative response of lymphocytes to T cell mitogens significantly increased after the diet containing 3.3% EPA + DHA. Interleukin 2 production significantly increased after the diets containing 1.3% and 3.3% EPA + DHA. No significant changes in mitogenic response or interleukin 2 production were found after ALA diets. Feeding 1.3% or 3.3% EPA + DHA or 5.3% ALA significantly suppressed prostaglandin E2 production in response to T cell mitogens. Plasma tocopherol concentrations were decreased significantly only in monkeys fed ALA diets. We conclude that after adjustment for the tocopherol concentration, marine-derived n-3 PUFAs but not plant-derived n-3 PUFAs increased T cell-mediated mitogenic response and interleukin 2 production. This is most likely due to diet-induced quantitative differences in cellular fatty acid composition and, thus, in prostaglandin E2 production and tocopherol status.