Showing papers by "Colorado State University published in 1991"

Methane and nitrous oxide fluxes in native, fertilized and cultivated grasslands

Abstract: Measurements of CH4 uptake and N2O emissions in native, nitrogen-fertilized, and wheat-growing prairie soils from spring to late autumn, 1990 are reported. It is found that nitrogen fertilization and cultivation can both decrease CH4 uptake and increase N2O production, thereby contributing to the increasing atmospheric concentrations of these gases.

Orthogonal Cultural Identification Theory: The Cultural Identification of Minority Adolescents

Abstract: A theory of cultural identification is presented indicating that identification with different cultures is orthogonal. Instead of cultures being placed at opposite ends of a continuum, cultural identification dimensions are independent of each other, and increasing identification with one culture does not require decreasing identification with another. Studies of Native-American and Mexican-American youth show that: (1) identification with Anglo (White American) culture is related to having Anglo friends and to family acceptance of an Anglo marriage, (2) identification with either the minority or the majority culture is a source of personal and social strength, and (3) this greater strength, however, does not translate automatically into less drug use, because drug use is related to how much the culture that the person identifies with approves or disapproves of drugs. [Translations are provided. See the International Abstracts at the end of the issue.]

Regulation of growth cone behavior by calcium.

Abstract: Few structures within the nervous system have received more attention than the neuronal growth cone. Initially named by Ramon y Cajal (1890) who recognized its dynamics and importance in histological sections, the growth cone plays essential roles in the development, repair, and modification of neuronal circuitry. Growth cones have a diverse repertoire of behaviors (Fig. 1). These behaviors underlie the more complex processes of neurite elongation, pathfinding, and selective synaptogenesis. Thus, a fundamental concern of developmental neurobiology is the definition of environmental and intracellular cues that regulate growth cone behavior. In this essay, we will consider the role of intracellular calcium in the regulation of growth cone behaviors. The impetus for envisaging such a role was provided by the elucidation of the calcium hypothesis of the control of secretion (Douglas, 1974, 1976) and synaptic transmission (Katz and Miledi, 1965; Katz, 1969; Llinas, 1979). Accordingly, we put forward a working hypothesis that stated, “if [intracellular] calcium falls below an optimal level, or rises significantly above it, growth cone motility and neurite outgrowth are inhibited” (Rater et al., 1988a).

Trishear fault-propagation folding

Abstract: Previous models of fault-propagation folding used kink-band geometries to approximate folding in front of propagating thrusts. However, kink-band kinematics cannot replicate the curved fold surfaces and complex strain patterns in natural and experimental fault-propagation folds, which also occur in front of steeper reverse and normal faults. Fault-propagation fold hinges tighten and converge downward, forming a triangular zone of penetrative deformation focused on the tip of the propagating fault. The downward convergence of deformation in fault-propagation folds can be modeled as triangular shear zones. "Trishear," here defined as distributed, strain-compatible shear in a triangular (in profile) shear zone, provides an alternate kinematic model for fault-propagation folds. Trishear is analogous to simple shear in a tabular shear zone except that area balance in a triangular shear zone requires curved displacement oblique to the fault slip direction. Incremental computer models of trishear folding can replicate many geometric features of fault-propagation folds, including variably curved fold hinges, downward-tightening fold surfaces, heterogeneous strains, and multiple fault-propagation trajectories.

Diffusion in Saturated Soil. I: Background

Abstract: Recent studies suggest that diffusion may be an important, if not dominant, mechanism of contaminant transport through waste containment barriers. This paper represents the first of two papers pert...

A new polarized atmospheric radiative transfer model

Abstract: A plane-parallel polarized radiative transfer model is described. The model is used to compute the radiance exiting a vertically inhomogeneous atmosphere containing randomly-oriented particles. Both solar and thermal sources of radiation are considered. A direct method of incorporating the polarized scattering information is combined with the doubling and adding method to produce a relatively simple formulation. Several numerical results are presented for verification and comparison.

Application of fast-Fourier-transform techniques to the discrete-dipole approximation.

Abstract: We show how fast-Fourier-transform methods can be used to accelerate computations of scattering and absorption by particles of arbitrary shape using the discrete-dipole approximation.

Mechanism of assembly of the tyrosyl radical-dinuclear iron cluster cofactor of ribonucleotide reductase.

Abstract: Incubation of the apoB2 subunit of Escherichia coli ribonucleotide reductase with Fe2+ and O2 produces native B2, which contains the tyrosyl radical-dinuclear iron cluster cofactor required for nucleotide reduction. The chemical mechanism of this reconstitution reaction was investigated by stopped-flow absorption spectroscopy and by rapid freeze-quench EPR (electron paramagnetic resonance) spectroscopy. Two novel intermediates have been detected in the reaction. The first exhibits a broad absorption band centered at 565 nanometers. Based on known model chemistry, this intermediate is proposed to be a mu-peroxodiferric complex. The second intermediate exhibits a broad absorption band centered at 360 nanometers and a sharp, isotropic EPR signal with g = 2.00. When the reaction is carried out with 57Fe2+, this EPR signal is broadened, demonstrating that the intermediate is an iron-coupled radical. Variation of the ratio of Fe2+ to B2 in the reaction and comparison of the rates of formation and decay of the intermediates to the rate of formation of the tyrosyl radical (.Y122) suggest that both intermediates can generate .Y122. This conclusion is supported by the fact that both intermediates exhibit an increased lifetime in a mutant B2 subunit (B2-Y122F) lacking the oxidizable Y122. Based on these kinetic and spectroscopic data, a mechanism for the reaction is proposed. Unlike reactions catalyzed by heme-iron peroxidases, oxygenases, and model complexes, the reconstitution reaction appears not to involve high-valent iron intermediates.

Theoretical CD studies of polypeptide helices: examination of important electronic and geometric factors.

Abstract: An improved model for calculating the CD of polypeptides has been developed. Excited state wavefunctions were derived from CNDO/S (complete neglect of differential overlap, spectroscopic) calculations on N-methylacetamide. Four discrete peptide-localized transitions were employed: pi 0 pi* (NV1), pi* + pi* (NV2), n pi*, and n' pi*. Inclusion of the pi + pi transition (lambda 0 = 140 nm) significantly improves the accuracy of the calculated CD spectra in the 180-250-nm region. Spectra were computed for various helical structures, including right-handed alpha-, alpha II-, omega-, pi-, 3(10-), and poly (proline) I-helices, and the left-handed poly (proline) II-helix. Sensitivity to changes in the peptide backbone geometry and chain length are examined. Electronic factors such as ground-state charge distribution, hybridization effects, and basis set deorthogonalization have been investigated. The nonconservative nature of the poly (Pro) I and II CD spectra is reproduced, and the helix band present in earlier exciton calculations on the alpha-helix has been diminished.

Diurnal Variability of the Hydrologic Cycle in a General Circulation Model

Abstract: In the present Colorado State University GCM simulation-based analysis of the diurnal and semidiurnal variability of precipitation, precipitable water, evaporation, cloudiness, horizontal moisture flux convergence, and cloud radiative forcing, a realistic afternoon precipitation maximum is obtained over land in warm rainy regions, as well as an early morning maximum over the oceans. The model has been further used to investigate the bases for the oceanic diurnal-precipitation cycle; the results thus obtained indicate that such an oceanic cycle occurs even in the absence of neighboring continents, and tends to have a morning maximum, although the observed phenomenon is generally stronger than the results indicate.

Fundamental Principles of Deception in Genetic Search

Abstract: This paper presents several theorems concerning the nature of deception and the central role that deception plays in function optimization using genetic algorithms. A simple proof is offered which shows that the only problems which pose challenging optimization tasks are problems that involve some degree of deception and which result in conflicting k-arm bandit competitions between hyperplanes. The concept of a deceptive attractor is introduced and shown to be more general than the deceptive optimum found in the deceptive functions that have been constructed to date. Also introduced are the concepts of fully deceptive problems as well as less strict consistently deceptive problems. A proof is given showing that deceptive attractors must have a complementary bit pattern to that found in the binary representation of the global optimum if a function is to be either fully deceptive or consistently deceptive. Some empirical results are presented which demonstrate different methods of dealing with deception and poor linkage during genetic search.

Heterogeneity of soil and plant N and C associated with individual plants and openings in North American shortgrass steppe

Abstract: Small-scale spatial heterogeneity of soil organic matter (SOM) associated with patterns of plant cover can strongly influence population and ecosystem dynamics in dry regions but is not well characterized for semiarid grasslands. We evaluated differences in plant and soil N and C between soil from under individual grass plants and from small openings in shortgrass steppe. In samples from 0 to 5 cm depth, root biomass, root N, total and mineralizable soil N, total and respirable organic C, C:N ratio, fraction of organic C respired, and ratio of respiration to N mineralization were significantly greater for soil under plants than soil from openings. These differences, which were consistent for two sites with contrasting soil textures, indicate strong differentiation of surface soil at the scale of individual plants, with relative enrichment of soil under plants in total and active SOM. Between-microsite differences were substantial relative to previously reported differences associated with landscape position and grazing intensity in shortgrass steppe. We conclude that microscale heterogeneity in shortgrass steppe deserves attention in investigation of controls on ecosystem and population processes and when sampling to estimate properties at plot or site scales.

Independent regulation of calcium revealed by imaging dendritic spines.

Abstract: THE dendritic spine is a basic structural unit of neuronal organization. It is assumed to be a primary locus of synaptic plasticity, and to undergo long-term morphological and functional changes1–6, at least some of which are regulated by intracellular calcium concentrations7–11. It is known that physiological stimuli can cause marked increases in intracellular calcium levels in hippocampal dendritic shafts12,13, but it is completely unknown to what extent such changes in the dendrites would also be seen by calcium-sensing structures within spines. Will calcium levels in all spines change in parallel with the dendrite or will there be a heterogeneous response? This study, through direct visualization and measurement of intracellular calcium concentrations in individual living spines, demonstrates that experimentally evoked changes in calcium concentrations in the dendritic shaft ([Ca2+]d) are frequently not parallelled in the spine ([Ca2+]s). This isolation is not caused by a physical diffusion barrier. This report provides, to our knowledge, the first direct demonstration of autonomous spine function.

Nonlinear Influence of Mesoscale Land Use on Weather and Climate

Abstract: It is shown that the influence of mesoscale landscape spatial variability on the atmosphere must be parameterized or explicitly modeled in larger-scale atmospheric model simulations including general circulation models. The mesoscale fluxes of heat that result from this variability are shown to be of the same order of magnitude but with a different vertical structure than found for the turbulent fluxes. These conclusions are based on experiments in which no phase changes of water were permitted. To parameterize surface thermal inhomogeneities, the influence of landscape must be evaluated using spectral analysis or an equivalent procedure. To include the nonlinear contribution of each scale, numerical model simulations for the range of observed surface and overlying atmospheric conditions must be performed.

Template synthesis of polymeric and metal microtubules

Abstract: : We describe in this report an elegant new method for the synthesis of organic microtubules. This new method is based on the use of a microporous membrane as a template during tubule synthesis. This template method produces tubules with monodisperse lengths and diameters, and length, diameter, and wall thickness can be varied at will. This type of precise control over tubule geometry is not possible with the existing synthetic method. The tubules obtained are composed of chemically and mechanically robust heterocyclic polymers. We have recently described a template method for the synthesis of organic microtubules. This method entails the use of the pores in a microporous membrane as templates for tubule formation. The key to the tubule-formation process is the presence of molecular anchors on the pore walls. These anchors insure that the tubule-forming materials deposits as a thin skin which lines the pore wall. We describe in this paper an electrochemical template method for the synthesis of metal (Au) microtubules. We also present a general paradigm for the formation of molecular anchors on the pore walls of alumina template membranes. We believe that this paradigm should allow for the synthesis of microtubules composed of any desired material.

Comparative aspects of osteosarcoma : dog versus man

Abstract: Canine osteosarcoma bears striking resemblance to osteosarcoma in humans. Similarities include the following: male sex predilection, large patient size, 75% or more affecting the appendicular site, metaphyseal location, generally unknown etiology, less than 10% of patients have documented metastasis at presentation, over 90% of tumors show high-grade histology, 75% of tumors show aneuploidy, the metastatic rate is 80% or more with amputation alone, the lung is the most common site of metastasis, and there is improved survival with adjuvant chemotherapy. The major differences are age of onset, with dogs being affected in middle age; greater frequency in the dog, with over 8000 new cases per year; and time to metastasis being faster in the dog than man. Canine osteosarcoma is a readily available and highly comparable spontaneously occurring cancer that should be useful in a better understanding of the same disease in humans.

The Behavior of Dense, Nonaqueous Phase Liquids in Fractured Clay and Rock

Abstract: This paper examines the behavior of dense, nonaqueous phase liquids (DNAPLs) in fractured clay and rock. The conditions under which a DNAPL will enter an initially water-saturated, rough-walled fracture are outlined and expressed in a number of ways, including the height to which a DNAPL pool can accumulate above a fracture prior to initial entry. To study the behavior of DNAPL in a rough-walled fracture following initial entry, numerical simulations are carried out both in the plane of a fracture using a discrete representation of fracture roughness, and at a larger scale of averaging using an equivalent homogeneous porous media approach. The simulations illustrate that DNAPL will migrate through the larger aperture regions of a fracture plane, and that the DNAPL has the potential to enter progressively smaller aperture fractures with depth as it migrates. Additional numerical simulations indicate that the time taken for a nonaqueous phase liquid to traverse a fractured aquitard is inversely proportional to the fracture aperture, the fracture dip from the horizontal, and the height of the pool collected above the aquitard. It is also demonstrated that upward hydraulic gradients across a fractured aquitard can significantly slow the downward rate of DNAPL migration while downward water gradients enhance the rate of DNAPL migration across the aquitard.

Medical problems of adult horses, as ranked by equine practitioners.

Abstract: This paper reports the results of a survey conducted among members of the American Association of Equine Practitioners, concerning medical problems of adult horses. A one-page questionnaire listing 36 medical problems grouped by body system was completed by 1,149 veterinarians. The top-ranked disease was colic, followed by viral respiratory tract disease, endometritis, dermatitis, and parasitism. When responses were evaluated by type of practice, location of practice, and number of veterinarians in the practice, ranking of the top 2 diseases was the same for the total respondents. Ranking of diseases 3 through 5 varied when these criteria were taken into consideration.

Diffusion in saturated soil. ii: results for compacted clay

Abstract: The effective diffusion coefficients, \ID\N*, of three anions (Br\u-, Cl\u-, and I\u-) and three cations (Cd²\u+, K\u+, and Zn²\u+) diffusing in two compacted clay soils, kaolinite and Lufkin clay, are measured. The ions are contained in a simulated waste leachate. The effects of molding water content and method of compaction on the measured \ID\N* values are evaluated for kaolinite. The calculated \ID\N* values varied between 4 × 10\u-¹\u0 m²/s and 2 × 10\u-\u9 m²/s and, based on the results for chloride diffusion in kaolinite, are relatively insensitive to molding water content and compaction method. The measured \ID\N* values for Cl\u- and Br\u- in kaolinite are in excellent agreement with previous studies, but the \ID\N* values for the cations are relatively high. High \ID\N* values for the cations are attributed to nonlinear adsorption behavior at relatively high concentrations and to the possibility of chemical precipitation of the heavy metal species (Cd²\u+ and Zn²\u+). Also, \ID\N* values determined from reservoir concentrations typically are higher than \ID\N* values determined from soil concentration profiles.

A Hypothetical Mechanism for Fetal Alcohol Syndrome Involving Ethanol Inhibition of Retinoic Acid Synthesis at the Alcohol Dehydrogenase Step

Abstract: Ethanol acts as a teratogen causing brain, craniofacial, and limb abnormalities in those suffering from fetal alcohol syndrome. Normal embryonic development of the vertebrate nervous system and limbs has recently been shown to be governed by retinoic acid, the active form of vitamin A. Retinol dehydrogenase is an enzyme needed to convert vitamin A (retinol) to retinoic acid, a molecule that specifies embryonic pattern formation by controlling gene expression. Ethanol acts as a competitive inhibitor of the retinol dehydrogenase activity attributed to mammalian alcohol dehydrogenase (ADH), an enzyme that uses both retinol and ethanol as substrates. An hypothesis is presented in which many of the abnormalities observed in fetal alcohol syndrome may be caused by high levels of ethanol acting as a competitive inhibitor of ADH-catalyzed retinol oxidation in the embryo or fetus. This would presumably result in a reduction of retinoic acid synthesis in embryonic tissues such as the nervous system and limbs that require critical levels of this molecule to specify spatial patterns.

The helix-coil transition in heterogeneous peptides with specific side-chain interactions: theory and comparison with CD spectral data.

Abstract: Natural and synthetic peptides that contain detectable intramolecular alpha-helical structure in aqueous solution have been used to evaluate the helical propensities for the common amino acids. Experimental spectroscopic data must be fit to a model of the helix-coil transition in order to determine quantitative stability constants for each amino acid. We present here a statistical mechanical description of helix formation in peptides or protein fragments that takes into account multiple internal conformations, heterogeneity in the stabilizing effects of different side chains, and specific side-chain-side-chain interactions. The model enables one to calculate values of [theta]222 for a given peptide using the length dependence of the helix signal computed by a quantum mechanical treatment of the n pi * transition that dominates the 222-nm band. In addition, the helical probability at any residue in the chain is readily computed, and should prove useful as nmr spectral data become available. The free energy of specific side-chain interactions, including ion pair formation, can be evaluated. Application of the analysis to experimental data on a pair of isomeric peptides, only one of which contains ion pairs, indicates that forming a single glutamate-lysine ion pair stabilizes the alpha-helix by 0.50 kcal/mole in 10 mM sodium ion and pH 7. A survey of the CD data measured for a variety of model peptides is presented, indicating that a single set of s values and sigma constant can account for some but not all of the available results.