2,321 research outputs found
Impact of acid atmosphere deposition on soils : field monitoring and aluminum chemistry
No full textThe effect of acid atmospheric deposition on concentrations and transfer of major solutes in acid, sandy soils was studied. Emphasis was given to mobilization and transport of potentially toxic aluminum. Data on solute concentrations and fluxes in meteoric water as well as soil solutions were obtained from intensive monitoring programmes conducted at a number of sites in northwestern Europe and North-America. Specific hypotheses were tested in laboratory experiments.Atmospheric acid inputs dominated total acid loads in nearly all soils studied. This was particularly true for forest soils in the Netherlands, due to an extreme dry deposition of (NH 4 ) 2 SO 4 in the forest canopy. Input of (NH 4 ) 2 SO 4 may acidify the soil, due to NH 4 assimilation, or nitrification of NH 4 and subsequent leaching of NO 3 .In soils rich in weatherable minerals, mobilization of base cations dominated acid neutralization, so that percolation water was buffered at relatively high pH values and the mobility of aluminum was low. In these soils the mobilization and transport of aluminum was mainly driven by organic acids, which is consistent with the podzolization theory. However, in soils depleted in weatherable minerals (e.g. most of the acid, sandy soils in the Netherlands), mobilization rates of base cations were too low for a substantial neutralization of atmospheric acidity, so that pH values of the percolation water were often low enough to cause a significant mobilization of aluminum. In these soils the atmospherically derived strong acid load was almost fully neutralized by aluminum dissolution. Much of this dissolved inorganic aluminum is currently lost to the groundwater.Although aluminum is abundant in soils only a minor fraction, largely consisting of non-silicate organically bound aluminum, formed in the course of soil development (podzolization), was readily dissolved. The current rapid and irreversible depletion of this fraction in many acid, sandy soils of the Netherlands constitutes a drastic change in soil genesis. Depletion may eventually also result in reduced acid neutralization, due to decreased dissolution of aluminum.The aluminum solubility control varied with soil depth. Surface soil solutions were highly undersaturated with respect to gibbsite solubility, whereas saturation was approached in the subsoil. Possibly, the low aluminum solubility in the surface soil was controlled by an exchange type equilibrium with organic soil aluminum. Insight in the aluminum solubility control in soils is not only relevant for improving our understanding of the aluminum chemistry in soils per se, but it may also help explaining the aluminum chemistry of surface water in mountainous catchments, where soil solutions may reach the stream via different flowpaths through the soil, depending on hydrological conditions
A narrative-based collaborative writing tool for coherent technical documents
No full textOne important feature of an effective document that makes it easy to read and understand is known as coherence. Technical documents produced collaboratively are often incoherent due to a lack of group consensus and misaligned contributions by the individual authors. However, current document planning techniques and writing tools do not provide explicit support for improving coherence. The goal of this research, therefore, is to develop and evaluate a new technique and tool that helps teams of authors to structure coherent technical documents. The coherence of a document can be attributed to the story (or narrative) it conveys to the reader. If this story is consistent and coherent, the same can be said about the document. A discourse theory such as Rhetorical Structure Theory (RST) that has been developed by linguists helps further to analyse and improve a narrative. RST explains the coherence of a text by virtue of relationships (such as “paragraph A justifies paragraph B”) between parts of the text. This research has combined the ideas from these parallel strands of research to develop a new document planning technique called narrative-based writing. The method involves writing down an explicit précis of the story (called a document narrative or DN) and then analysing it using RST. The DN and RST analysis are then used to structure the eventual document. To extend the usability of narrative-based writing to geographically-dispersed authors, I have designed and implemented a collaborative tool that allows co-authors to edit, analyse and review DNs. The thorough design for the tool uses a combination of three models (conceptual, business process and functional) culminating in a set of functions that enable collaborative narrative-based writing. This dissertation discusses how, in the future, these functions could be incorporated in existing collaborative writing tools. Implementing this tool, albeit in its current prototypic state, has been invaluable in understanding the complexities of modelling and manipulating DNs and RST structures. Initial investigations using the new technique and tool have been positive, encouraging me to continue the research and evaluation in this field
Evaluatie suppleties Noord-Holland en Texel
No full textNote: NH-93.ANV002a.pdf bevat het hoofdrapport en NH-93.ANV002b.pdf bevat alle bijlagen. ----- De minister van Verkeer en Waterstaat heeft de kamer een interim-nota kustverdediging in 1993 toegezegd, waarin het kustverdedigingsbeleid wordt geëvalueerd. Een onderdeel van deze evaluatie is de evaluatie van de zandsuppleties. Om deze evaluatie uit te voeren is de werkgroep EVAZAND, onder leiding van de Dienst Getijdewateren, ingesteld. De evaluatie beperkt zich in principe tot de morfologische aspecten en is hoofdzakelijk gericht op het bepalen van de doelmatigheid of de effectiviteit van zandsuppleties. Omdat suppleties van 1990 of later zich vanwege de korte levensduur nauwelijks lenen voor evaluatie is een selectie gemaakt uit de suppleties van vóór 1990. Deze nota dient als de bijdrage van de Directie Noord-Holland aan het project EVAZAND en bevat de evaluatie van alle grote zandsuppleties van Noord-Holland en Texel van vóór 1990.EVAZAN
Dehydrogenation of the NH−NH Bond Triggered by Potassium tert-Butoxide in Liquid Ammonia
No full textA novel strategy for the dehydrogenation of NH-NH bond is disclosed using potassium t-butoxide (tBuOK) in liquid NH3 under air (O2) at room temperature. Its synthetic values are well demonstrated via highly efficient synthesis of aromatic azo compounds (up to 100% yield, 3 min), heterocyclic azo compounds, and dehydrazination of phenylhydrazine. The broad application of this strategy and its benefit to chemical biology is proved by a novel, convenient, one-pot and efficient synthesis of aliphatic diazirines, which are important photoreactive agents for photoaffinity labeling
Molecular tagging velocimetry of NH fluorescence in a high-enthalpy rarefied gas flow
No full textIn this paper a new type of molecular tagging velocimetry based on NH fluorescence was developed and validated for the velocity measurements of a high-enthalpy rarefied gas wind tunnel where the maximum flow velocity exceeds 6 km/ s near the nozzle exit at 0.2 Pa. The feasibility of this technique using the short-lived NH fluorescence was demonstrated in the hypersonic rarefied gas flow with yielding velocity profiles at multiple downstream locations from the nozzle exit. The total uncertainty of the measured flow velocities was estimated to be less than 6% when the flow velocity is above 2000 m/ s. For the new tagging technique only a single laser and a single time-gated camera are required for velocity measurement due to the existence of NH radicals in the arc-discharged-N2 mixed with a small amount of H-2. Therefore the NH-MTV not only shows great promise for tagging in high-enthalpy rarefied gas of nitrogen or air flows without seeding but also possesses high practicability and facility for velocity measurement
Un lema a revisar en Plinio, NH XXXII 149
No full textAt Plinius, NH XXXII 149, the author conjetures ...lepus... lupus... for ...elepris... lepus....No disponible
Effect of combined nitrogen on symbiotic nitrogen fixation in pea plants
No full textThe nitrogen-fixing activity of the symbiotic system of Pisum sativum with Rhizobium leguminosarum is adversely affected by combined nitrogen. Both ammonium chloride and potassium nitrate, when added to the roots, lower the nitrogenase activity (acetylene-reduction) of intact pea plants. During a 3-day treatment of the plants with combined nitrogen, when the in vivo nitrogenase activity falls to less than 50%, the nitrogenase activity of isolated bacteroids, treated with toluene and supplied with ATP and reductants, does not decrease. Thus, the potential nitrogenase activity of the root nodules is unaffected by short-term combined-nitrogen treatment of the plants. The adverse effect of ammonium chloride on the nitrogenase activity of pea plants is counteracted by the addition of sucrose or of methionine sulfoximine (an inhibitor of ammonia assimilation) to the rooting medium. A higher light intensity also diminishes the effect of ammonium chloride on nitrogenase activity.Ammonium chloride has no specific inhibitory effect on the nitrogenase activity of isolated pea bacteroids, neither in the anaerobic, nor in the aerobic assay. On the other hand, ammonium chloride does inhibit the nitrogenase activity of detached root nodules within a few hours. At a lower oxygen concentration in the assay this inhibition is more pronounced. The effect of ammonium chloride on detached nodules is relieved by simultaneous addition of methionine sulfoximine.Various carbon compounds (glucose and tricarboxylic acid cycle intermediates) stimulate the nitrogenase activity of detached nodules; only dicarboxylic acids of the tricarboxylic acid cycle support the nitrogenase activity of isolated bacteroids. Efficiencies of nitrogen fixation as to consumption of carbon compound are similar in both system , although lower than in the intact system. Ammonium chloride does not affect respiratory activities of detached nodules or of isolated bacteroids.It is concluded from the above-mentioned results that combined nitrogen, added to intact plants or detached nodules, does not affect nitrogenase activity directly. The results support the photosynthate theory, i.e. the photosynthate supply of the nodules is reduced and consequently the nitrogenase activity decreased, owing to the consumption of carbon compounds for the assimilation of the added combined nitrogen
INTRAMOLECULAR NH \ldots N HYDROGEN BONDS
No full textAuthor Institution: Department of Chemistry, University of CalgarySpectroscopic evidence for intramolecular NH \ldots N hydrogen bonds in o-phenylenediamines, ethylenediamine, and the monocations of sparteine-and -isosparteine- N-oxides will be presented. Integrated intensity measurements, frequency measurements, and deuteration studies in the fundamental NH stretching region in dilute solution show evidence for intramolecular NH . . . N hydrogen bonds in o-phenylenediamines. Partial deuteration shows that the two NH bonds of a given amino group are nonequivalent, but that the two -NHD groups are identical, suggesting a conformation in which each amino group acts as both a proton donor and a proton acceptor. Similar studies on compounds where , etc., will be discussed with special reference to the conformation of ethylenediamine. In the monocations of sparteine- and -isosparteine-N-oxide the geometry of the system leads to very strong intramolecular hydrogen bonds, which remain unbroken even in dimethylsulphoxide solution
THE VALENCE STATES OF NH
No full textAuthor Institution: LOS Alamos Scientific Laboratory, University of CaliforniaTheoretical results from various levels of configuration interaction calculations are presented for the and states of the NH radical. In addition to spectroscopic constants for each state, dipole moments and transition moments between electronic states are reported
FOURIER-TRANSFORM SPECTROSCOPY OF NH AND NH IN THE NEAR-INFRARED
No full textAuthor Institution: Laboratoire Interuniversitaire des Systemes Atmospheriques (LISA), CNRS and Universites Paris-7 et -12, Creteil, France; Laboratorio de Espectroscopia e Laser, Instituto de Fisica, Universidade Federal Fluminense, Niteroi, Rio de Janeiro, BrazilThe near-infrared absorption spectrum of NH is an interesting opportunity for atmospheric {\it in-situ} measurements of this species using tuneable diode-lasers. For this purpose, accurate line positions and intensities are indispensable. In the past, several studies of the absorption spectrum of NH in the near-infrared were carried out, using Fourier-transform and tuneable diode-laser spectroscopy. More recently, high-resolution diode-laser spectra of NH were analyzed for the first time. The lines of NH in this region are also useful for wavenumber calibration of absorption spectra obtained with tuneable lasers. In our group, we have recently investigated the possibility to detect atmospheric NH using photoacoustic laser spectroscopy in the 1.5 m region, and observed several discrepancies between individual line positions and intensities observed in our and previous studies, as already noticed by other groups. In order to solve this problem we have measured new absorption spectra of NH (and also of NH) in the 6300-7500 cm region using a Bruker IFS 120-HR Fourier-transform spectrometer. The length of the absorption cell was 30 cm. The NH pressures employed were around 30 mbar, and the spectral resolution used was 0.02 cm, leading to linewidths (Full-Width at Half-Maximum) of about 0.03 cm. Based on these spectra, we have produced a list of individual line positions and line intensities at 296 K. Comparisons with the previous studies will be presented. }, {\bf 162}, 230-245 (1993).} }, {\bf 40}, 2031-2042 (2004).} }, {\bf 45}, 31-45 (2004).} }, {\bf 28}, 59-66 (2004).} }, in press (2006).
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