Showing papers by "University of Colorado Boulder published in 1981"

Self-interaction correction to density-functional approximations for many-electron systems

Abstract: The exact density functional for the ground-state energy is strictly self-interaction-free (i.e., orbitals demonstrably do not self-interact), but many approximations to it, including the local-spin-density (LSD) approximation for exchange and correlation, are not. We present two related methods for the self-interaction correction (SIC) of any density functional for the energy; correction of the self-consistent one-electron potenial follows naturally from the variational principle. Both methods are sanctioned by the Hohenberg-Kohn theorem. Although the first method introduces an orbital-dependent single-particle potential, the second involves a local potential as in the Kohn-Sham scheme. We apply the first method to LSD and show that it properly conserves the number content of the exchange-correlation hole, while substantially improving the description of its shape. We apply this method to a number of physical problems, where the uncorrected LSD approach produces systematic errors. We find systematic improvements, qualitative as well as quantitative, from this simple correction. Benefits of SIC in atomic calculations include (i) improved values for the total energy and for the separate exchange and correlation pieces of it, (ii) accurate binding energies of negative ions, which are wrongly unstable in LSD, (iii) more accurate electron densities, (iv) orbital eigenvalues that closely approximate physical removal energies, including relaxation, and (v) correct longrange behavior of the potential and density. It appears that SIC can also remedy the LSD underestimate of the band gaps in insulators (as shown by numerical calculations for the rare-gas solids and CuCl), and the LSD overestimate of the cohesive energies of transition metals. The LSD spin splitting in atomic Ni and $s\ensuremath{-}d$ interconfigurational energies of transition elements are almost unchanged by SIC. We also discuss the admissibility of fractional occupation numbers, and present a parametrization of the electron-gas correlation energy at any density, based on the recent results of Ceperley and Alder.

Host-Pathogen Interactions : XIX. THE ENDOGENOUS ELICITOR, A FRAGMENT OF A PLANT CELL WALL POLYSACCHARIDE THAT ELICITS PHYTOALEXIN ACCUMULATION IN SOYBEANS.

Abstract: An elicitor of phytoalexin accumulation (endogenous elicitor) is solubilized from purified cell walls of soybean (Glycine max [L.] Merr., cv. Wayne) by extracting the walls with hot water or by subjecting the walls to partial acid hydrolysis. The endogenous elicitor obtained from soybean cell walls binds to an anion exchange resin. The elicitor-active material released from the resin contains oligosaccharides rich in galacturonic acid; small amounts of rhamnose and xylose are also present. The preponderance of galacturonic acid in the elicitor-active fragments suggests that the elicitor is, in fact, a fragment of a pectic polysaccharide. This possibility is supported by the observation that treatment of the wall fragments with a highly purified endopolygalacturonase destroys their ability to elicit phytoalexin accumulation. This observation, together with other evidence presented in this paper, suggests that galacturonic acid is an essential constituent of the elicitor-active wall fragments. Endogenous elicitors were also solubilized by partial hydrolysis from cell walls of suspension-cultured tobacco, sycamore, and wheat cells.

The cause and cure (!) of the spurious pressures generated by certain fem solutions of the incompressible Navier‐Stokes equations: Part 2

Abstract: SUMMARY The spurious pressures and ostensibly acceptable velocities which sometimes result from certain FEM approximate solutions of the incompressible Navier-Stokes equations are explained in detail. The concept of pressure modes, physical and spurious, pure and impure, is introduced and their effects on discretized solutions is analysed, in the context of both mixed interpolation and penalty approaches. Pressure filtering schemes, which are capable of recovering useful pressures from otherwise polluted numerical results, are developed for two particular elements in two-dimensions and one element in three-dimensions. The automatic pressure filter associated with the penalty method is also explained. Implications regarding the effect of spurious pressure modes on accuracy and ultimate convergence with mesh refinement are discussed and a list of unanswered questions presented. Sufficient numerical examples are discussed to corroborate the theory presented herein.

Investigation of the flexibility of DNA using transient electric birefringence.

Abstract: In the preceding article, a Monte Carlo analysis was presented which provides a quantitative numerical relationship between the rotational diffusion coefficients, as measured by the decay of optical anisotropy following an electric field pulse, and the flexibility (persistence length) of short, wormlike chains. In the present article, the results of the foregoing analysis are applied to the observed rates of decay of birefringence for a series of sequenced DNA fragments ranging in size from 104 to 910 base pairs. Under the conditions used in this study, the DNA fragments exist as native, duplex molecules. Furthermore, conditions are defined in which the observed relaxation times are not dependent on DNA concentration, field strength, or the duration of the pulse. It is pointed out that the ionic atmosphere associated with a wormlike polyion does not exert any significant (direct) influence on the rotational diffusion of the polyion and, therefore, that the rotational relaxation times are a true measure of the configurations of the DNA molecules in solution. Moreover, excluded-volume effects are shown not to be significant for the moderately short molecules employed in this study. The major conclusion of this study is that there is no strong ionic strength dependence of the persistence length for ionic strengths above 1 mM and that the persistence length, under conditions where electrostatic contributions are negligible, is approximately 500 A. For ionic strengths significantly lower than 1 mM, electrostatic contributions to the stiffness of DNA become significant.

Zitterbewegung and the internal geometry of the electron

Abstract: Schr\"odinger's work on the Zitterbewegung of the free electron is reexamined. His proposed "microscopic momentum" vector for the Zitterbewegung is rejected in favor of a "relative momentum" vector, with the value $\stackrel{\ensuremath{\rightarrow}}{\mathrm{P}}=mc\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\alpha}}$ in the rest frame of the center of mass. His oscillatory "microscopic coordinate" vector is retained. In the rest frame, it takes the form $\stackrel{\ensuremath{\rightarrow}}{\mathrm{Q}}=\ensuremath{-}i(\frac{\ensuremath{\hbar}}{2mc})\ensuremath{\beta}\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\alpha}}$, and the Zitterbewegung is described in this frame in terms of $\stackrel{\ensuremath{\rightarrow}}{\mathrm{P}}$, $\stackrel{\ensuremath{\rightarrow}}{\mathrm{Q}}$, and the Hamiltonian $m{c}^{2}\ensuremath{\beta}$, as a finite three-dimensional harmonic oscillator with a compact phase space. The Lie algebra generated by $\stackrel{\ensuremath{\rightarrow}}{\mathrm{Q}}$ and $\stackrel{\ensuremath{\rightarrow}}{\mathrm{P}}$ is that of SO(5), and in particular $[{Q}_{i},{P}_{j}]=\ensuremath{-}i\ensuremath{\hbar}{\ensuremath{\delta}}_{\mathrm{ij}}\ensuremath{\beta}$. It is argued that the simplest possible finite, three-dimensional, isotropic, quantum-mechanical system requires such an SO(5) structure, incorporates a fundamental length, and has harmonic-oscillator dynamics. Dirac's equation is derived as the wave equation appropriate to the description of such a finite quantum system in an arbitrary moving frame of reference, using a dynamical group SO(3,2) which can be extended to SO(4,2). Spin appears here as the orbital angular momentum associated with the internal system, and rest-mass energy appears as the internal energy in the rest frame. Possible generalizations of these ideas are indicated, in particular those involving higher-dimensional representations of SO(5).

Long-term stress-induced analgesia and activation of the opiate system.

Abstract: Exposure of rats to a series of inescapable shocks produced in sequence both an early naltrexone-insensitive and a late naltrexone-reversible analgesic reaction. Activation of the opiate system was...

An analysis of associative learning in a terrestrial mollusc

Abstract: We have recently demonstrated that associative learning can play an important role in the regulation of food selection behavior ofLimax maximus, a terrestrial mollusc. The tendency ofLimax to approach a normally attractive odor generated by a food source such as carrot or potato can be markedly reduced if exposure to that odor is paired with exposure to a bitter taste (quinidine sulfate). We now report that variables known to influence associative learning by vertebrates (the operations of a second-order conditioning procedure, blocking and US-pre-exposure) similarly influence associative learning byLimax.

Genetic variation in space and time in a population of ponderosa pine

Abstract: The genetic structure of a population of Pinus ponderosa was studied using seven electrophoretically-detectable protein loci. This population is composed of six groups of trees, which differ significantly from each other in their genetic constitutions. The results imply that the population is composed of groups of individuals assembled into genetically-related family units. Whenever such family clusters have been documented in other studies, marked inbreeding has also been noted as a consequence. In this population, no inbreeding is detectable. The groups also differ from one another in several characteristics which have genetic consequences within the population as a whole. These characteristics include age structures, seed output, level of infestation by woolly aphids and extent of damage by deer browsing. The population was also divided into four age classes which do not differ markedly from one another in their genetic characteristics. This suggests that genetic differentiation in time is much less marked than differentiation in space.

Monte Carlo approach to the analysis of the rotational diffusion of wormlike chains

Abstract: Synopsis A Monte Carlo analysis is presented which establishes a relationship between the rotational diffusion coefficients and the flexibility (persistence length, P) of short, wormlike chains. The results of this analysis are presented in terms of experimentally observable quantities; namely, the rotational relaxation times for the field-free decay of optical anisotropy. The pertinent theoretical quantity is R, defined as the ratio of the longest rotational relaxation time of a wormlike chain to the transverse rotational relaxation time of a rigid cylinder having the same axial length (L) and segmental volume. R, so defined, is essentially independent of the axial ratio of the cylinder for any value of LIP within the range of validity of the present analysis (axial ratio > 20; 0.1 < L/P < 5). It is pointed out that P can be determined with reasonable accuracy even in the absence of a precise knowledge of the local hydrodynamic radius of the chain.

Late Quaternary Environmental History of Lake Valencia, Venezuela

Abstract: Chemical, paleontological, and mineralogical analyses of a 7.5-meter core from the middle of Lake Valencia, Venezuela, have provided information on the paleoclimatic history of this low-elevation, low-latitude site for the last 13,000 years. The data show that dry climates existed in this region from 13,000 years before present (B.P.) until about 10,000 years B.P. The Lake Valencia Basin was occupied by intermittent saline marshes at that time. About 10,000 years B.P., a permanent lake of fluctuating salinity formed and arboreal plant communities replaced the earlier dominant xeric herbaceous vegetation and marsh plants. By 8500 years B.P., Lake Valencia reached moderate to low salinities and discharged water; the modern vegetation became established at that time. After 8500 years B.P., the lake twice ceased discharging as a result of reduced watershed moisture. The second of these drying episodes is still in progress and has been aggravated by human activities in the watershed.

Shear-Induced Melting

Abstract: The collective translational structure of dilute suspensions (\ensuremath{\sim} 0.1% by weight) of charged, spherical, and colloidal particles under shear is investigated by light scattering. When subjected to increasing shear rate, the equilibrium bcc Wigner lattice exhibits two major, reversible, disordering transitions. Transition II occurs at low shear, is kink mediated and results in freely slipping two-dimensional hcp layers. At higher rates, transition I occurs where these two-dimensional layers melt via shear-induced fluctuations (phonons) to produce an amorphous structure. The amorphous structure has stringlike particle correlations which ultimately disappear.

Host-Symbiont Interactions: V. THE STRUCTURE OF ACIDIC EXTRACELLULAR POLYSACCHARIDES SECRETED BY RHIZOBIUM LEGUMINOSARUM AND RHIZOBIUM TRIFOLII

Abstract: The sequence of the glycosyl residues and the anomeric configurations of the glycosyl linkages of the acidic polysaccharides secreted by Rhizobium leguminosarum 128c53, Rhizobium leguminosarum 128c63, Rhizobium trifolii NA30, and Rhizobium trifolii 0403 have been determined. All four polysaccharides were found to have the following glycosyl repeating-unit structure, where galactosyl is Gal, glucosyl is Glc, glucuronosyl is GlcA, and pyruvyl is Pyr: [Formula: see text] Each of the glycosyl residues of these polysaccharides was determined to be in the d configuration and in the pyranose ring form. These results add support to the proposal that R. leguminosarum and R. trifolii have a particularly close genetic relationship. The significance of these results with regard to the possible function of these polysaccharides in the nodulation process is discussed.

A precise inter-procedural data flow algorithm

Abstract: Data flow analysis is well understood at the intra-procedural level and efficient algorithms are available. When inter-procedural mechanisms such as recursion, procedure nesting, and pass-by-reference aliasing are introduced, the data flow problems become much more difficult. The avail, live, and must-summary data flow problems are shown to be NP-complete in the presence of aliasing. However, an algorithm is presented with O(SET*EDGE) time performance where EDGE is the size of the program's flow graph and SET is a possible exponential number which reflects the number of aliasing patterns of the program. It is argued that in practice SET is small and on the order of the number of variables of the program.

Approaches to Encouraging Conservation Behavior: A Review and Conceptual Framework

Abstract: This paper introduces a conceptual framework aimed at integrating the conservation behavior literature and facilitating the comparison of findings across studies. Within this framework, conservation behavior is approached from the theoretical orientations of attitude change, behavior modification and behavior maintenance. Seven commonly used approaches to encouraging conservation behavior are described in terms of these perspectives. Illustrative research related to each approach is reviewed.

A New Look at the Discrete Ordinate Method for Radiative Transfer Calculations in Anisotropically Scattering Atmospheres

Abstract: The difficulties inherent in the conventional numerical implementation of the discrete ordinate method (following Chandrasekhar's prescription) for solving the radiative transfer equation are discussed. A matrix formulation is developed to overcome these difficulties, and it is specifically shown that the order of the algebraic eigenvalue problem can be reduced by a factor of 2. An expression for the source function is derived and used to obtain angular distributions. By appealing to the reciprocity principle, it is shown that substantial computational shortcuts are possible if only integrated quantities such as albedo and transmissivity are required. Comparison of fluxes calculated by the present approach with those obtained by other methods shows that low-order discrete ordinate approximations yield very accurate results. Thus, the present approach offers an efficient and reliable computational scheme that lends itself readily to the solution of a variety of radiative transfer problems in reali...

Hot oxygen atoms in the upper atmosphere of Venus

Abstract: Using data obtained by an ultraviolet spectrometer on the Pioneer-Venus Orbiter, energy and altitude distribution of nonthermal oxygen atoms in the Venus atmosphere for typical daytime and nighttime conditions are calculated using two different numerical methods. Agreement is found between results obtained by the two-stream transport method and the diffusion equation technique. Dissociative recombination of molecular oxygen ions and charge exchange of atomic oxygen ions with the neutral hydrogen and oxygen gas are the source terms, and calculations show that the dissociative recombination term is the dominant one. It is shown that measured hot atom concentrations exceed estimates of the thermal hydrogen atom concentrations derived from Brinton et al. (1980) over most of the daytime exosphere, and the calculated concentrations do so to an even greater extent. It is concluded that hot oxygen atoms are an important component of the dayside exosphere of Venus, their most important effect being the absorption of solar wind.

Identification of Mauthner-initiated response patterns in goldfish: Evidence from simultaneous cinematography and electrophysiology

Abstract: 1. This paper demonstrates that the Mauthner (M-) cell action potential is correlated with the onset of C-type fast-start responses beginning with a contraction of the contralateral body musculature. We made extracellular recordings from individual M-cells with chronically implanted microelectrodes in six goldfish while the animals were free to swim in an aquarium (19–23 °C). Fast-start responses were elicited by dropping a ball into the aquarium from above the fish. The behavior was filmed at 500 frames/s with a high-speed cine camera (Fig. 31). 2. In 45 responses, the M-cell action potential (M-spike) fired 7.4 ms ±6.7 (±SD) after the ball hit the water. The M-spike was followed after 8.1 ms±1.6 by the first stage of a C-type fast-start response that began with an initial contraction of the body on the side opposite the monitored M-cell (Figs. 5 A and 6). This is consistent with neuroanatomical and physiological evidence that the M-cell excites contra-lateral motor neurons. No M-spike was recorded in 18 trials when the C-start began with an initial contraction on the same side as the monitored M-cell (Fig. 7B1, 7B2). Presumably, such responses were initiated by the unmonitored M-cell on the opposite side of the brain. There was also no M-spike when the fish did not respond to the stimulus (ten trials). 3. M-initiated C-starts fell into two different response categories differentiated by the turns taken during the second stage of the motor pattern. In most cases (83%) the animal continued in the trajectory of its initial turn (Fig. 5 A). In 17% of the responses the second stage turn was in a direction opposite that taken initially, so that the animal darted forward (Fig. 5B). 4. The maximum mean displacement speed of three fish in 21 trials was 18 body lengths/s as measured from the rostrum. This occurred at about 16 ms after the response began (Fig. 9A). The maximum mean angular velocity of the head was 3,500 deg/s. This occurred at 10 ms after the response began (Fig. 9C). These values correspond to the pronounced lateral movement of the head during the initial stage of the response. 5. The M-initiated first stage was Stereotypic in terms of the trajectory taken (Fig. 8) and the mechanical performance of the animal (Fig. 9 B and D). In contrast, the turning performance during the second stage was variable from trial to trial (Figs. 8, 9B and D). 6. M-initiated responses were directed away from the stimulus. The M-cell on the side closest to the ball was the one that usually fired (85% of the trials) so that the initial turn was away from the stimulus. During 87% of the second stage responses, the animal oriented away from the stimulus (Fig. 10).

An in-place, in-order prime factor FFT algorithm

Abstract: This paper presents a Fortran program that calculates the discrete Fourier transform using a prime factor algorithm. A very simple indexing scheme is employed that results in a flexible, modular algorithm that efficiently calculates the DFT in-place. A modification of this algorithm gives the output both in-place and in-order at a slight cost in flexibility. A comparison shows it to be faster than both the Cooley-Tukey algorithm and the Winograd nested algorithm.