Showing papers by "University of California, San Diego published in 1975"

Random-Field Instability of the Ordered State of Continuous Symmetry

Abstract: Phase transitions are considered in systems where the field conjugate to the order parameter is static and random. It is demonstrated that when the order parameter has a continuous symmetry, the ordered state is unstable against an arbitrarily weak random field in less than four dimensions. The borderline dimensionality above which mean-field-theory results hold is six. (auth)

Notes on a schema for stories

Abstract: Publisher Summary The chapter discusses that the structure of stories is ordinarily more than pair wise relationships among sentences, and strings of sentences combine into psychological wholes. It also explains the nature of these wholes and presents a simple story grammar that accounts for many of the salient facts about the structure of simple stories and that will serve as the basis for a theory of summarization. The grammar consists of a set of syntactical rules that generate the constituent structure of stories and a corresponding set of semantic interpretation rules that determine the semantic representation of the story. The symbol “+” is used to form two items in a sequence; the symbol “|” is used to separate mutually exclusive alternatives. A “*” following a structure name indicates one or more of those units; for example, A* is one or more As. In the semantic structures the convention is followed that the predicate names are written in the ovals and the arguments of the predicates are pointed to by arrows. The propositions that are the units of the story are simply numbered.

An Application of Normal Mode Theory to the Retrieval of Structural Parameters and Source Mechanisms from Seismic Spectra

Abstract: A cyclic process of refining models of the mechanical structure of the Earth and models of the mechanism of one or more earthquakes is developed. The theory of the elastic-gravitational free oscillations of the Earth is used to derive procedures for resolving nearly degenerate multiplets of normal modes. We show that a global network of seismographs (W.W.S.S.N.) permits resolution for angular orders l ≤ 76 and for frequencies a) w ≤ 0.090 s -1 . The peak or centre frequency of each nearly degenerate multiplet is interpreted to be a gross Earth datum. Together, the data are used to refine models of the mechanical structure of the Earth. The theory of free oscillations is used further to derive procedures for retrieving the mechanism, or moment tensor, of an earthquake point source. We show that a globa network of seismographs permits retrieval for frequencies 0.0125 s-1 ≤ w ≤ 0.0825 s-1 . We show that refined models of structure and mechanism lead to improved resolution and retrieval, and that an array of sources further complements the resolution of multiplets. We present a ‘standardized dataset’ of 1064 distinct, observed eigenfrequencies ol the elastic-gravitational free oscillations of the Earth. These gross-Earth data are compiled from 1461 modes reported in five studies: 2 modes reported by Derr (1969), 159 modes observed by Brune & Gilbert (1974), 240 modes observed by Mendiguren ( 1973), 248 modes observed by Dziewonski & Gilbert (1972,1973) and 812 modes reported here. It is our opinion that the establishment of a standardized dataset should precede the establishment of a standardized model of the Earth. Two new Earth models are presented that are compatible with the modal data. One is derived from model 508 (Gilbert & Dziewonski 1973) and the other from model B1 (Jordan & Anderson 1974). In the outer core and in the lower mantle, below a depth of about 950 km, the differences between the two models are negligibly small. In the inner core there are minor differences and in the upper mantle there are major differences in detail. The two models and the modal data are compatible with traditional ray data, provided that appropriate baseline corrections are made to the latter. The source mechanisms, or moment tensors, of two deep earthquakes, Colombia (1970 July 31) and Peru-Bolivia (1963 August 15), have been retrieved from the seismic spectra. In both cases the moment tensor possesses a compressive (implosive) isotropic part. There is good evidence that isotropic stress release begins gradually, over 80s before the origin time derived from the onset of short-period P and S waves. During the process of stress release the principal axes of the moment rate tensor migrate. The axis of compression is relatively stable, the compressive stress rate is dominant, and the other two axes rotate about the axis of compression. We speculate that earthquakes, occurring deep within descending lithospheric plates, are not sudden shearing movements alone but do exhibit compressive changes in volume such as would be associated with a phase change. We further speculate that compressive changes in volume may occur without sudden shearing movements, that there may be 9 silent earthquakes’.

Self-inhibition by dopaminergic neurons.

Abstract: Animals and Plants, L. E. Gilbert and P. H. Raven, Eds. (Univ. ofTexas Press, Austin, 1975), p. 3. 76. J. W. Hanover, Annu Rev. Entomol. 20,75 (1975). 77. R. H. Smith, U.S. For. Serv. Gen. Tech. Rep. PSW-I (1972); A. A. Berryman, BioScience 22, 598 (1972). 78. V. 1. Grimal'skii, L. T. Krushev, V. P. Gorlushkina, Lesn. Khoz. 12, 54 (1971); W. P. Smeljanez and L. A. Chursin, Anz. Schaedlingskd. 45, 33 (1972). 79. C. M. McKell, J. P. Blaisdell, J. R. Goodin, Eds., Wildland Shrubs-Their Biology and Utilization (General Technical Report INT-1, U.S. Forest Service, Washington, D.C., 1972). 80. C. H. A. Little, Can. J. Bot. 48, 1995 (1970). 81. S. J. Dina and L. G. Klikoff, J. Range Manage. 26, 207 (1973); J. D. Hodges and P. L. Lorio, Jr., Can. J. Bot. 47, 1651 (1969); see also Parker (84). 82. D. Otto, Arch. Forstwes. 19, 135 (1970). 83. W. Schwenke, Z. Angew. Entomol. 61, 365 (1968). 84. J. Parker, in Water Deficits and Plant Growth, T. T. Kozlowski, Ed. (Academic Press, New York, 1972), vol. 3, p. 125. 85. A. W. Naylor, in ibid., p. 241; R. E. Saunier, H. M. Hull, J. H. Ehrenreich, Plant Physiol. 43, 401 (1968). 86. T. C. R. White, Oecologia 16,279 (1974). 87. G. T. Harvey, Can. Entomol. 106, 353 (1974); see also Otto (82) and Schwenke (83). 88. T. T. Kozlowski, J. For. 67, 118 (1969); H. 0. Batzer, Environ. Entomol. 2, 727 (1973). 89. D. H. Janzen, Am. Nat. 104, 501 (1970); C. B. Huffaker, in Dynamics of Populations, P. J. denBoer and G. R. Gradwell, Eds. (Centre for Agricultural Publishing and Documentation, Wageningen, Netherlands, 1971), p. 327; J. R. Blais, For. Chron. 44 (1968).

The effects of contextual scenes on the identification of objects.

Abstract: This experiment demonstrates the influence of the prior presentation of visual scenes on the identification of briefly presented drawings of real-world objects. Different pairings of objects and scenes were used to produce three main contextual conditions: appropriate, inappropriate, and no context. Correct responses and confusions with visually similar objects depended strongly on both the contextual condition and the particular target object presented. The probability of being correct was highest in the appropriate context condition and lowest in the inappropriate context condition. Confidence ratings of responses were a function of the perceptual similarity between the stimulus object and the named object; they were not strongly affected by contextual conditions. Morton's (1970) "logogen" model provided a good quantitative fit to the response probability data.

Experimental properties of superfluid He 3

Abstract: This paper presents a summary and evaluation of the experimental properties of superfluid $^{3}\mathrm{He}$ as they were known in the fall of 1974. Subjects having thermodynamic significance, including specific heat, static magnetism, phase equilibria, and superfluid density, are discussed first. Then known flow properties are treated. After a brief discussion of the theoretical ideas which motivated some of the later experiments, the subject of dynamic magnetism is reviewed. Closely related work in a magnetic field in the immediate temperature region of the critical temperature is discussed, as are the propagation of ultrasound, the phenomena of supercooling and superheating, precise indication of the critical temperature, and the effects of certain restrictive geometries. The article concludes with a brief discussion of some new developments which appeared after the main text was finished. Appendices on thermometry and on parameters of the normal Fermi liquid are included.

Popular Culture and High Culture: An Analysis and Evaluation Of Taste

Abstract: Herbert Gans offers a critique of the universality of high cultural standards. While conceding that popular and high culture have converged to some extent, he still holds that the division exists.

Some principles of memory schemata

Abstract: Publisher Summary A fundamental aspect of the structure of material contained within a large, intelligent memory system is that the contexts, in which units of the stored information are accessed, are critically important in determining the way that information is interpreted and used. Most of the schemes, currently under active consideration, can be viewed as variants of list structures or semantic network structures. This chapter discusses some implications of these memory structures in regard to how the connections among different memory units are formed and interpreted, and some of the issues of processing that arise when these memory structures are used. It also discusses the nature of memory reference processes that can lead automatically, without particular effort, to the richness of the retrievals that it is believed to be a fundamental property of human memory. When two or more processes use the same resources at the same time, they may both interfere with one another, neither may interfere with the other, or one may interfere with a second without any interference from the second process to the first. The important principle is that a process can be limited in its performance either by the amount of available processing resources, such as memory or processing effort, or by the quality of the data available to it. Competition among processes can affect a resource-limited process, but not a data-limited one.

Lung tumors in mice: application to carcinogenesis bioassay.

Abstract: Publisher Summary This chapter provides information on lung tumors in mice, with emphasis on the use of mouse lung for quantitative investigations in carcinogenesis, especially bioassay of chemicals for carcinogenic activity. The lung-tumor response in strain A mice is easily and clearly positive to all major types of chemical carcinogens. Strain A mice are the most susceptible to a wide variety of carcinogens, in terms of the earlier appearance and greater multiplicity of tumors. The lung-tumor response in strain A mice is easily and clearly positive to all major types of chemical carcinogens. Estrogenic and other steroid hormones, with the targets of endocrine-regulated tissues, are an exception. The lung tumor of the mouse has demonstrated its ability to pick up undetected, unpredicted neoplastic responses such as to urethane and to isoniazid. The carcinogens picked up by the lung tumor system have been shown to be carcinogenic for other tissues and in other species of animals. The mouse lung tumor is a reproducible, stable, and rapid biological model for a wide variety of quantitative investigations in carcinogenesis. It provides a three-dimensional lattice of the lung in which a known, identifiable subpopulation of cells—the type 2 alveolar pneumocytes—can be accelerated into conversion into neoplasms.

The Fetal Alcohol Syndrome

Abstract: A specific pattern of malformation involving prenatal-onset growth deficiency, developmental delay, craniofacial anomalies, and limb defects is now recognized in offspring of chronic alcoholic women. Historical evidence suggests that this is not a new observation. A recent French study of 127 offspring of alcoholic mothers indicates that this specific syndrome has been recognized in other parts of the world. Many of the features of this disorder could be related to the kind of malorientation of brain structure seen at the autopsy of one patient described herein. The frequency (43%) of adverse outcome of pregnancy for chronic alcoholic women suggests that serious consideration be given to early termination of pregnancy in severely chronic alcoholic women.

Membrane fluidity and cellular functions.

Abstract: An area of intense current interest in molecular and cell biology is the structure of biological membranes. A great change in our picture of membranes has occurred in the last few years, and there is now fairly widespread acceptance of a model for the organization of the lipids and proteins of membranes called the “fluid mosaic model” (Singer and Nicolson, 1972). In this model (Fig. 1) the proteins that are integral to the membrane (Singer, 1971) are proposed to be globular molecules which are partly embedded in the membrane lipid, and partly protrude from it. This partial embedding is determined thermodynamically by the amphipathic character of the integral protein molecule; its hydrophobic end is embedded in the hydrophobic membrane interior and its hydrophilic end protrudes into the aqueous phase. The lipid, arranged largely as a bilayer, forms the matrix of the membrane, and since at physiological temperatures the lipid of most functional membranes is largely fluid, the integral proteins are in principle free to move about laterally and rapidly in the plane of the membrane. There is now a very substantial body of evidence that is consistent with, and strongly supports, the fluid mosaic model. The discussion of this evidence could easily occupy my entire presentation, but I thought that in the context of this symposium it might be more useful to adopt the model as a working hypothesis of membrane structure and consider what it might imply about the mechanisms of a variety of important cellular functions and activities.

Effects of changes in preload, afterload and inotropic state on ejection and isovolumic phase measures of contractility in the conscious dog.

Abstract: Despite much investigation, the usefulness of various indexes employed clinically for detecting alterations in ventricular contractility in the intact circulation remains controversial. The effects of acute preload, afterload and contractility changes on both ejection and isovolumic phase measures of left ventricular function were analyzed in normal, trained conscious dogs instrumented with micromanometers and endocardial ultrasonic diameter gauges. Rapid volume overload increased the excursion of the left ventricular diameter (Δ LVD) by 7 percent above the control level, but mean velocity of circumferential shortening (V CF ) did not change significantly; peak rate of left ventricular pressure rise (dP/dt) increased by 11 percent and (dP/dt)/DP40 (DP = developed pressure) was augmented by 10 percent, but maximal [(dP/dt)/LVP], or "V pm " decreased by 20 percent. Pressure overload by phenylephrine infusion decreased Δ LVD by 15 percent and mean V CF fell by 26 percent; peak dP/dt and (dP/dt)/DP40 remained unaltered, but V pm was reduced by 37 percent. Isoproterenol augmented peak dP/dt by 55 percent, and (dP/dt)/DP40, V pm and mean V CF were increased comparably. Propranolol decreased these measures equally by about 16 percent. Therefore, in the conscious animal in the steady state, isovolumic phase indexes were mildly influenced by acute volume loading, whereas ejection phase indexes were not. Acute increases in aortic pressure markedly reduced ejection phase measures, whereas the isovolumic indexes were unaffected. All of the indexes studied were comparably sensitive to acute alterations in contractility, but we conclude that no single measure can always be used for defining an acute contractility change in the intact circulation.

Study of the sensitivity of coupled reaction systems to uncertainties in rate coefficients. III. Analysis of the approximations

Abstract: In Parts I and II of this series [J. Chem. Phys. 59, 3873, 3879 (1973)] we developed a new method of sensitivity analysis for large sets of coupled nonlinear equations with many parameters. In developing this theory and in carrying out the computer calculations involved in this analysis we made a number of approximations. We present here a quantitative analysis of these approximations and, where applicable, develop rigorous error bounds. Our analysis shows that we can specify the approximations which enter into our theory so as to obtain sensitivity measures of known accuracy. On this basis we feel that the techniques developed in this series of papers provide a useful and efficient method of sensitivity analysis of large systems with many parameters.

Hippocampal innervation by serotonin neurons of the midbrain raphe in the rat.

Abstract: The organization of the brainstem serotonin neuron projection to the hippocampal formation was analyzed in the rat. This projection arises in the raphe nuclei of the midbrain. Following destruction of the midbrain raphe nuclei, chiefly nucleus centralis superior, there is a 72% decrease in hippocampal serotonin content. Injection of tritiated amino acid into the midbrain raphe nuclei results in transport of tritiated protein to the hippocampal formation and this transport is blocked in animals pretreated by intraventricular administration of 5,6-dihydroxytryptamine (5,6-DHT). Autoradiographic analysis indicates that the transport reaches the hippocampal formation primarily via two major pathways, the cingulum and the fornix. Cingulum fibers terminate predominantly in the dorsal hippocampus whereas the fornix distributes throughout the entire hippocampal formation. Some fibers reach the ventral hippocampus from the entorhinal area. Within the hippocampus there is dense labeling in a restricted lamina of the CA1 stratum lacunosum-moleculare with moderate labeling in stratum radiatum. Stratum oriens is sparsely labeled in CA1 and moderately so in CA2 and CA3. Stratum radiatum and stratum lacunosum-moleculare are moderately densely labeled in CA2 and Ca3. The area dentata is sparsely to moderately labeled in the molecular layer and heavily labeled in a thin lamina of the hilar zone immediately beneath the granule cell layer. The remaining hilar zone is moderately labeled. All of the discrete labeling of the hippocampus and area dentata described above is absent in animals pretreated with 5,6-DHT. These observations indicate that serotonin neurons of the midbrain raphe provide a highly organized innervation of the hippocampal formation in the rat.

Nonthermal Processes in Large Solar Flares

Abstract: In many small solar flares the ~10–100 keV electrons accelerated during the flash phase contain the bulk of the total flare energy output. In large flares, such as those in the period 1972, August 2–7, the flash phase electrons are present in substantially greater numbers. These electrons can explosively heat the chromosphere-lower corona and eject flare material. The ejected matter can produce a shock wave which will then accelerate nucleons and electrons to relativistic energies. We analyze energetic particle, radio, X-ray, gamma ray and interplanetary shock observations of the 1972 August flares to obtain quantitative estimates of the energy contained in each facet of these large flares. In general these observations are consistent with the above hypothesis. In particular: (1) From the X-ray emission (van Beek et al., 1973) the energy contained in > 25 keV electrons is calculated to be≳ 2 × 1032 erg for the 1972, August 4 event. Since the lower energy cutoff to the electron spectrum is known to be below 25 keV and possibly below 10 keV, the electrons contain enough energy to produce the following interplanetary shock wave, which has by far the bulk of the energy dissipated in the flare. Similar numbers are obtained for the large August 7 flare event. (2) From the γ-ray emission (Chupp et al., 1973) the energy in protons dumped at the same level of the atmosphere, assuming a thick target situation, is at least a factor of three smaller than the electrons. Moreover the γ-ray emission indicates that the bulk of the protons are accelerated at least several minutes after the electrons. Thus it is more likely that the electrons are responsible for the flare optical (Hα and white light) emissions which occur in the chromosphere. (3) Approximately 5% of the electrons and≳ 99% of the protons escape into the interplanetary medium to be observed by spacecraft. This situation is consistent with the hypothesis of shock acceleration of the protons high in the solar corona. (4) The four most intense X-ray bursts observed during the period July 31—August 11 are the only bursts followed by an interplanetary shock wave and a new injection of energetic protons into the interplanetary medium.

Susceptibility of interconfiguration-fluctuation compounds

Abstract: We present a simple model for the magnetic susceptibility of rare-earth compounds which exhibit interconfiguration fluctuations (ICF). It is shown that the temperature dependence of the magnetic susceptibility of several ICF Yb compounds can be fitted quantitatively, assuming an energy separation ${E}_{\mathrm{ex}}$ between the two configurations and an intrinsic lifetime $\ensuremath{\tau}$ due to the $4f$-shell-conduction-electron interaction. With the parameters ${E}_{\mathrm{ex}}$ and $\ensuremath{\tau}$ obtained from such fits it is possible to predict the temperature dependence of the valence.

Effects of polyunsaturated fats on lipid metabolism in patients with hypertriglyceridemia.

Abstract: Studies were carried out on the effects of polyunsaturated fats on lipid metabolism in 11 patients with hypertriglyceridemia. During cholesterol balance studies performed in eight patients, the feeding of polyunsaturated fats, as compared with saturated fats, caused an increased excretion of endogenous neutral steroids, acidic steroids, or both in most patients. Increases in steroid excretions were marked in some patients and generally exceeded the decrement of cholesterol in the plasma compartment. The finding of a greater excretion of fecal steroids on polyunsaturated fats in hypertriglyceridemic patients contrasts to the lack of change in sterol balance previously reported for patients with familial hypercholesterolemia; however, other workers have found that polyunsaturated fats also enhance steroid excretion in normal subjects. In most of the patients, simultaneous studies were carried out on biliary lipid composition, hourly outputs of biliary lipids, and pool sizes of bile acids. In several but not all patients, fasting gallbladder bile became more lithogenic after institution of polyunsaturated fats. This increased lithogenicity was not due to a decrease in bile acid pools; in no case was the pool decreased by polyunsaturated fats. On the other hand, two patients showed an increased output of biliary cholesterol, and frequently there was an increase in fecal neutral steroids that were derived from cholesterol; thus, polyunsaturated fats may increase bile lithogenicity in some patients through mobilization of cholesterol into bile. Reductions in plasma cholesterol during the feeding of polyunsaturated fats was seen in most patients, and these changes were usually associated with a decrease in concentration of plasma triglycerides. In fact, the degree of cholesterol lowering was closely correlated with the extent of triglyceride reduction. Therefore, in hypertriglyceridimec patients polyunsaturated fats may contribute to cholesterol reduction by changing the metabolism of triglycerides or very low density lipoproteins. The findings of changes in the metabolism of cholesterol, bile acids, and triglycerides in the patients of this study suggests that polyunsaturated fats may cause a lowering of cholesterol through multiple mechanisms, and it seems unlikely that a single action can explain all the effects of these fats on the plasma lipids.