Discussion Of Equilibrium Research Articles

Concurrent and Coplanar Forces that Are in Equilibrium

If a body is in equilibrium under the action of three non-parallel coplanar forces, the forces must be concurrent, that is, must meet at a single point. Specific examples are provided here to illustrate the validity of this statement by the use of free-body diagrams as well as during the discussion of equilibrium and moments. These cases are usually not presented in contemporary textbooks; hence, it is our intention to provide examples to help in visualizing the concept. A discussion about four coplanar forces is included.

The concept(s) and controversies of equilibrium

Equilibrium is one of the key concepts not only in economics, but in social science in general as well as the natural sciences. However, in no other field has it received, to my knowledge, such a central role, nor drawn as much sharp criticism. It’s claimed to be indispensible for economic modelling and theorizing, and yet at the same time it’s a major target for criticism. A recent debate about the concept has resulted in a number of articles and books on the topic, taking widely different stands on how equilibrium is to be understood, its role in economic theory and methodology, and what this role means for economics as a science. This book is a welcome and valuable contribution to this debate. The book has three parts. The first one deals with how economics has borrowed equilibrium concepts and methods from the natural sciences, the second with how equilibrium was conceptualised and used by some early economic theorists, and the third with issues concerning equilibrium in modern economic theory. The general impression from a first reading is of the immense number of different concepts grouped together as ‘‘the’’ concept of equilibrium, and the reader is left with a greater appreciation of why discussions of equilibrium in economics often become so confused. However, the book also raises crucial questions about the role of economics as a science, about the role of theories and models, and their relation to the real world which we aim to explain.

Formation of Methionine from α-Amino-n-Butyric Acid and 5′-Methylthioadenosine in the Rat

Adult rats may utilize two metabolites of methionine for the biosynthesis of this essential amino acid. In separate experiments methionine, labeled with 14C or with 35S was observed in plasma and urine following the administration of [2-14C]-alpha-amino-n-butyric acid or [35S]-5'-methylthioadenosine by stomach tube. Although alpha-amino-n-butyric acid (ABA) or homoserine, alone or with dietary sodium sulfate, choline, and/or S-methylcysteine, was not utilized for growth, weight loss in weanling rats was decreased by dietary cysteine when fed as an additive to a basal methionine-free, cysteine-free, labile methyl-free, sulfur-free diet. Following the addition of 10 mg ABA and 28 mg 5'-methylthioadenosine/day to the basal diet, growth response was equivalent to that occurring in rats receiving 27 mg of methionine/day with the basal diet. The implications of these findings for adaptation to protein restriction and a discussion of equilibrium and steady state conditions related to the increase in methionine content in the blood are presented.

A self-consistent two-dimensional approach to magnetospheric structures

A simple self-consistent description of the geomagnetic tail is given and its consequences are explored. The model is two-dimensional, ignoring the spatial variation along the direction of the tail current. A discussion of equilibria is based on the assumption of an isotropic pressure. One of the conclusions is that the transition between the dipolar and the tail region will take place over a fairly short distance. The analytical results are supplemented by a numerical example. Properties of configurations containing field line loops are investigated. A stability discussion includes the effect of the net magnetic flux through the neutral sheet. The results have consequences for current magnetospheric problems.