7 Matching Results

Search Results

Advanced search parameters have been applied.


Description: How did life come to be on the surface of the earth? Darwin himself recognized that his basic idea of evolution by variation and natural selection must be a continuous process extending backward in time through that period in which the first living things arose and into the period of 'Chemical Evolution' which preceded it. We are approaching the examination of these events by two routes. One is to seek for evidence in the ancient rocks of the earth which were laid down prior to that time in which organisms capable of leaving their skeletons in the rocks to be fossilized were in existence. This period is sometime prior to approximately 600 million years ago. The earth is believed to have taken its present form approximately 4700 million years ago. We have found in rocks whose age is about 1000 million years certain organic molecules which are closely related to the green pigment of plants, chlorophyll. This seems to establish that green plants were already fluorishing prior to that time. We have now found in rocks of still greater age, namely, 2500 million years, the same kinds of molecules mentioned above which can be attributed to the presence of living organisms. If these molecules are as old as the rocks, we have thus shortened the time available for the generation of the complex biosynthetic sequences which give rise to these specific hydrocarbons (polyisoprenoids) to less than 2000 million years.
Date: June 1, 1965
Creator: Calvin, Melvin
Partner: UNT Libraries Government Documents Department


Description: 'Ethyl metaphosphate' or tetrapolyphosphate esters are a potentially useful starting material for the preparation of polynucleotides. The kinetics of the reactions of the esters with excess water and ethanol have been measured by means of p{sup 31} n.m.r. and IR spectroscopy. Upon the addition of specific amounts of water or ethanol, substances could be prepared which consist mainly of linear tetrapoly-, tripoly- or pyrophosphate esters containing smeller amounts of other polyphosphates and orthophosphates in an equilibrium composition. Diethyl hydrogen orthophosphate reacts with cyclic polyphosphate esters to open the ring; with linear esters it reacts to form polyphosphates with a lesser degree of condensation. This latter reaction also proceeds to an equilibrium. No reactions between linear and cyclic polyphosphate esters were observed at room temperature, which implies that the rates of the disproportionation of the linear polyphosphate esters were low. Some organic solvents previously employed for the dehydrating polymerization of sugars, amino acids or nucleotides destroy the tetrapolyphosphate esters. The various substances now available from tetrapolyphosphate esters by the action of water or reactive solvents will differ in their capabilities of producing the dehydrating polymerization reaction. Thus, one may expect that very different products might result from very small differences in reaction conditions.
Date: March 1, 1965
Creator: Burkhardt, Gottfried; Klein, Melvin P. & Calvin, Melvin.
Partner: UNT Libraries Government Documents Department


Description: EARLIER investigations have demonstrated that di-cyandiamide (DCDA), the dimer of cyanamide, can successfully promote the dehydration condensation of: (1) glucose and orthophosphate to give glucose-6-phosphate; (2) adenosine and orthophosphate to give adenosine-5'-monophosphate; (3) orthophosphate to give pyrophosphate; (4) alanine to give alanylalanine and alanylalanylalanine. These reactions were carried out in dilute aqueous solutions in the dark. (It was also demonstrated that the combination of ultra-violet light and dicyandiamide could promote the synthesis of dipeptides. This observation has since been confirmed by other investigators.) These experiments were designed to demonstrate one possible means by which such compounds could have been formed on the prebiotic Earth, thus providing materials needed for the origin of living systems. Dicyandiamide itself could have been, present on the primitive Earth as was demonstrated with the ultra-violet irradiation of cyanide solution.
Date: April 1, 1965
Creator: Steinman, Gary; Kenyon, Dean H. & Calvin, Melvin
Partner: UNT Libraries Government Documents Department


Description: Using infra-red spectroscopy, the equilibrium exchange times have been determined for a series of ketones, aromatic aldehydes, and {beta}-ketoesters reacting with oxygen 18 enriched water. These exchange times have been evaluated in terms of steric and electronic considerations, and applied to a discussion of the exchange times of chlorophylls a and b and chlorophyll derivatives.
Date: December 1, 1965
Creator: Byrn, Marianne & Calvin, Melvin
Partner: UNT Libraries Government Documents Department


Description: The purpose of this paper is twofold: to introduce the reader to the subject of instabilities exhibited by relativistic particle beams, and to summarize the present state of our knowledge concerning these phenomena. Most of the material in the first part of the paper is not new. It has been known to some specialists for a good many years; what is new is that the problems that can be solved are now of much more interest to the general community of accelerator physicists. Consequently, many accelerator physicists who have not paid much attention to these matters may now want to become informed; it is my hope that this paper will provide an introduction to the field. The second part of the article consists of two sections. The first summarizes the experimental information presently available, with emphasis upon the degree to which it confirms or disagrees with theory. Our current level of understanding is delineated: considering the generality and reliability of the theoretical analysis as well as the degree of experimental confirmation, the author expresses his opinion as to what can be considered relatively well established. The final section contains a discussion of subjects needing further investigation and, consequently, supplements the discussion of areas of understanding by describing the peripheral areas of uncertainty.
Date: October 4, 1965
Creator: Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department


Description: This is the first of two papers in which the low-temperature properties of liquid He{sup 3} are to be calculated in the thermodynamically consistent 'T-matrix' approximation. The set of coupled integral equations which are to be solved is exhibited in Part A of this paper. Part B of this paper is devoted to a preliminary, zero-temperature calculation which employs the additional approximations of using separable potentials and a noninteracting spectral function to define the interaction of two particles in the medium: the <T>{sub 0} approximation. In this approximation they obtain a spectral function for the quasi particles which they expect to display general features in common with those of the actual spectral function. Using this spectral function, they calculate the thermodynamic properties of the system and find that they compare favorably to those obtained in other calculations.
Date: November 17, 1965
Creator: Beck, Donald E. & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department


Description: The vapors of potassium, rubidium, and cesium have been photoionized with light absorbed in the discrete region of the atomic spectrum. The energy threshold for the ionization process has been determined and the ions produced identified by mobility measurements. The data give lower limits for the dissociation energies of K{sup +2}, Rb{sup +2} and Cs{sup +2}. Each of these molecular ions has a bond energy approximately 50% greater than that of the corresponding neutral molecule. In addition, lower limits for the electron affinities of the alkali atoms and approximate values for the mobilities of Rb{sup +} and Rb{sup +2} in rubidium vapor are given.
Date: February 1, 1965
Creator: Lee, Yuan-tseh & Mahan, Bruce H.
Partner: UNT Libraries Government Documents Department