bluuebunny/crossref_metadata_2025 huggingface dataset:
A topographic index approach for identifying groundwater habitat of young-of-year brook trout (Salvelinus fontinalis) in the landlake ecotone
Authors: Borwick Jason , Buttle Jim , Ridgway Mark S
Published: January 2006

We used a topographic index (TI) approach to link the presence of young-of-year (YOY) brook trout (Salvelinus fontinalis) at groundwater seepage and stream sites in the landlake ecotone with subwatershed topography surrounding a set of 21 lakes in Algonquin Provincial Park, Ontario. A lakeshore site's TI value was positively related to the temperature difference between the substrate and lake surface, indicating higher TI values were associated with greater groundwater input. YOY brook trout tended to occupy lakeshore sites with relatively large TI values. Groundwater habitat available to YOY brook trout was relatively rare, with only a few sites used consistently on an annual basis. Larger lakes had fewer groundwater habitat sites per unit length of shoreline than smaller lakes. Logistic regression analysis and model selection (via Akaike's Information Criterion) indicated the odds of finding YOY brook trout increased significantly when a site was a stream and, in the summer, when there was a large difference in temperature between lake substrate and lake surface. Most of the stream sites used by brook trout were not on the Ontario base map system but were revealed by the TI approach.
Forecasting effects of climate change on Great Lakes fisheries: models that link habitat supply to population dynamics can help
Authors: Jones Michael L , Shuter Brian J , Zhao Yingming , Stockwell Jason D
Published: January 2006

Future changes to climate in the Great Lakes may have important consequences for fisheries. Evidence suggests that Great Lakes air and water temperatures have risen and the duration of ice cover has lessened during the past century. Global circulation models (GCMs) suggest future warming and increases in precipitation in the region. We present new evidence that water temperatures have risen in Lake Erie, particularly during summer and winter in the period 19652000. GCM forecasts coupled with physical models suggest lower annual runoff, less ice cover, and lower lake levels in the future, but the certainty of these forecasts is low. Assessment of the likely effects of climate change on fish stocks will require an integrative approach that considers several components of habitat rather than water temperature alone. We recommend using mechanistic models that couple habitat conditions to population demographics to explore integrated effects of climate-caused habitat change and illustrate this approach with a model for Lake Erie walleye (Sander vitreum). We show that the combined effect on walleye populations of plausible changes in temperature, river hydrology, lake levels, and light penetration can be quite different from that which would be expected based on consideration of only a single factor.
Nonlocal conserved currents for the modified chiral model in (2 + 1) dimensions
Authors: Zait R A , Mourad M F , Abdel-Wahab N H
Published: January 2006

We show that the technique of Brezin et al. for constructing nonlocal conserved currents for 2-dimensional models can be extended to certain special models in (2 + 1) dimensions. We construct an infinite number of these currents for the modified chiral model in (2 + 1) dimensions. We obtain general expressions for the corresponding charges. In addition, we derive an alternative linear system for this model from our constructed nonlocal currents. We highlight some features of our modelling and offer comments. PACS Nos.: 02.30.Jr, 03.40.Kf, 03.65.Ge, 05.45.Yv
Atomic X-ray spectroscopy of accreting black holes
Authors: Liedahl D A , Torres D F
Published: January 2006

Current astrophysical research suggests that the most persistently luminous objects in the Universe are powered by the flow of matter through accretion disks onto black holes. Accretion disk systems are observed to emit copious radiation across the electromagnetic spectrum, each energy band providing access to rather distinct regimes of physical conditions and geometric scale. X-ray emission probes the innermost regions of the accretion disk, where relativistic effects prevail. While this has been known for decades, it also has been acknowledged that inferring physical conditions in the relativistic regime from the behavior of the X-ray continuum is problematic and not satisfactorily constraining. With the discovery in the 1990s of iron X-ray lines bearing signatures of relativistic distortion came the hope that such emission would more firmly constrain models of disk accretion near black holes, as well as provide observational criteria by which to test general relativity in the strong field limit. Here, we provide an introduction to this phenomenon. While the presentation is intended to be primarily tutorial in nature, we aim also to acquaint the reader with trends in current research. To achieve these ends, we present the basic applications of general relativity that pertain to X-ray spectroscopic observations of black hole accretion-disk systems, focusing on the Schwarzschild and Kerr solutions to the Einstein field equations. To this, we add treatments of the fundamental concepts associated with the theoretical and modeling aspects of accretion disks, as well as relevant topics from observational and theoretical X-ray spectroscopy.PACS Nos.: 32.30.Rj, 32.80.Hd, 95.30.Dr, 95.30.Sf, 95.85.Nv, 97.10.Gz. 97.80.Jp, 98.35.Mp, 98.62.Mw
Black-hole boundaries
Authors: Booth Ivan
Published: January 2006

Classical black holes and event horizons are highly nonlocal objects, defined in relation to the causal past of future null infinity. Alternative, quasilocal characterizations of black holes are often used in mathematical, quantum, and numerical relativity. These include apparent, Killing, trapping, isolated, dynamical, and slowly evolving horizons. All of these are closely associated with two-surfaces of zero outward null expansion. This paper reviews the traditional definition of black holes and provides an overview of some of the more recent work on alternative horizons.PACS Nos.: 04.20.Cv, 04.70.s, 04.70.Bw
A modal solution for reflection and transmission at a ChiralChiral interface
Authors: Crittenden P E , Bahar E
Published: January 2006

A harmonic Green's function solution for a magnetic line source above and below a flat interface between two chiral materials is derived. The solution is expressed in terms of the characteristic right and left circularly polarized waves. The harmonic Green's function formulation is converted into a modal representation. The modal representation is suitable for the complete expansion of the electromagnetic fields above and below a rough interface between two chiral materials with laterally varying material properties. The modal expansion is written in terms of orthogonal-basis and reciprocal-basis functions, which have been used to formulate generalized Fourier transforms and derive the generalized telegraphists' equations for electromagnetic fields in irregular chiral media.PACS Nos.: 33.55.Ad, 78.20.Ek
Finite element simulation of seismically induced retrogressive failure of submarine slopes
Authors: Azizian A , Popescu R
Published: January 2006

Retrogressive failures have been reported for both offshore and onshore slopes subjected to various triggering mechanisms. As a result of large spatial extension of the failure, the retrogression phenomenon leads to significantly increasing damage and may affect facilities located far away from the original slope. The mechanisms of such failures are not fully understood, and reports of analyses are rather scarce. To simulate earthquake-induced retrogressive submarine slope failures and to better understand the mechanisms involved, the element removal capabilities of a finite element program are used to model a soil mass that fails and then flows away, causing upper parts of the slope to fail retrogressively, as a result of the loss of support. It is explained how an initial failure leads to subsequent failures of a flat seafloor. Effects of a shallow silt layer and of a gently sloping seafloor on the extension of retrogression in a sandy seabed are also studied. It is found that the extension of failure increases significantly because of a gentle seafloor slope and (or) the presence of a silt layer.Key words: retrogressive submarine failure, seismic liquefaction, finite elements.
Application of an effective stress design method to concrete piles driven in Mexico City clay
Authors: Saldivar Emilio E , Jardine Richard J
Published: January 2006

Piled foundations are used widely in the lake clay zones of Mexico City, with “friction” piles being driven into soft diatomaceous clay deposits that show an extraordinary range of mechanical properties. The paper assesses the applicability of the Imperial College pile (ICP) design method to the concrete piles driven in these deposits. After the ICP methodology and Mexico City ground conditions are reviewed, an experimental study is reported of the key soil properties required for the ICP procedures: yield stress ratio, unit weight, interface friction angle (δ), sensitivity (St), and intrinsic properties. The new data are then applied to a specially assembled database of static pile load tests from different Mexico City clay locations, with allowance being made for site-specific details and local installation procedures. A quantitative assessment shows that the ICP methodology is free from significant bias and leads to more reliable estimates of static capacity than the total stress (α) design method routinely used in Mexico City.Key words: validation, database, static axial pile capacity, driven friction pile, effective stress design, silty clay.
A study of hysteresis models for soil-water characteristic curves
Authors: Pham Hung Q , Fredlund Delwyn G , Barbour S Lee
Published: January 2006

A review of hysteresis models for soil-water characteristic curves is presented. The models can be categorized into two groups: (i) domain models (or physically based models) and (ii) empirical models. Some models are capable of predicting scanning curves, while other models are capable of predicting the boundary wetting curve and the boundary drying curve. A comparison of the ability of five selected models to predict the boundary wetting curve showed that the Feng and Fredlund model with enhancements by Pham, Fredlund, and Barbour appears to be the most appropriate model for engineering practice. Another comparison among five physically based models for predicting scanning curves showed that the Mualem model-II gives the best overall prediction of scanning curves. The study showed that taking the effect of pore blockage into account does not always give a better prediction of hysteretic soil-water characteristic curves. A scaling method for estimating the initial drying curve, the boundary wetting curve, and the boundary drying curve is also presented in the paper.Key words: soil-water characteristic curve, hysteresis model, comparison, boundary curve, scanning curve, unsaturated soils.
A field study on the behavior of a foundation underpinned by micropiles
Authors: Han Jie , Ye Shu-Lin
Published: January 2006

Micropiles have been used for many applications, including underpinning existing foundations to support structures subjected to additional loads, such as stories added to buildings. A field study was conducted to simulate a footing initially constructed on a natural soil to support a structure and later subjected to additional loads. This study investigated load transfer mechanisms during the connection of micropiles to the concrete plate under the initial load and during the additional loading. Earth pressure cells and rebar strain gauges were installed underneath the loading plate and in the micropiles, respectively, to monitor variation of stresses during the loading and connection processes. The behavior of micropiles in the underpinned foundation under the additional loading was analyzed and compared with that in the single-micropile loading tests presented in a companion paper. Theoretical solutions were adopted for examining the results obtained from this field study, including the overall stiffness of the underpinned foundation, the tip resistance, and the ratio of the load carried by the plate (raft). Guidelines are proposed for designing underpinned foundations using micropiles subjected to additional loads.Key words: underpinning, micropile, load transfer, skin friction, tip resistance, piled raft.
A field study on the behavior of micropiles in clay under compression or tension
Authors: Han Jie , Ye Shu-Lin
Published: January 2006

Micropiles have been used for underpinning existing foundations founded on problematic soil, disturbed by the intrusion of underground activities (such as tunneling), or subjected to additional loads (such as stories added to existing buildings). This paper presents a field study on the behavior of single micropiles in soft clay subjected to compression or tension. Two compression and two tension loading tests were conducted on four single micropiles. All the micropiles were instrumented with rebar strain gauges, and they were monitored during the progress of loading. To set up a baseline for underpinned loading tests presented in a companion paper, a full-scale loading test was performed on natural soil. The results from all these full-scale loading tests are presented and analyzed in this paper. The paper discusses loaddisplacement responses, elastic moduli, axial forces, tip resistance, and skin friction relating to micropiles and their interactions with soft clay. Theoretical solutions for bearing capacity of soil, load capacity of piles, and percentage of tip resistance to the total load were adopted for examination of the test results.Key words: micropile, loaddisplacement, load capacity, skin friction, tip resistance.
Kinetics and mechanism of the oxidation of alcohols by tetrapropylammonium perruthenate
Authors: Chandler W David , Wang Zhao , Lee Donald G
Published: January 2006

2-Propanol is oxidized by tetrapropylammonium perruthenate (TPAP) in a reaction that is second order in TPAP and first order in 2-propanol. One of the products, believed to be ruthenium dioxide, is an effective catalyst for the reaction, making it an autocatalytic process. The rate of oxidation is relatively insensitive to the presence of substituents. Primary kinetic deuterium isotope effects are observed when either the hydroxyl or the α hydrogen is replaced by deuterium. The only product obtained from the oxidation of cyclobutanol is cyclobutanone, indicating that the reaction is a two-electron process. Tetrahydrofuran is oxidized at a rate that is several orders of magnitude slower than that observed for 2-propanol, suggesting that the reaction of TPAP with alcohols may be initiated by formation of perruthenate esters. A tentative mechanism consistent with these observations is proposed.Key words: oxidation, alcohols, tetrapropylammonium perruthenate, reaction mechanism, autocatalysis.
Kinetics and mechanism of acid-catalyzed hydrolysis of the diazo functional groups of 1-diazo-2-indanone and 2-diazo-1-indanone in aqueous solution
Authors: Chiang Yvonne , Kresge A Jerry , Sadovski Oleg , Zeng Xiaofeng , Zhu Yu
Published: January 2006

Rates of hydrolysis of 1-diazo-2-indanone and 2-diazo-1-indanone were measured in dilute aqueous perchloric acid solutions using both H2O and D2O as the solvent, and rates of hydrolysis of the latter substrate were measured in dilute aqueous (H2O only) formic acid buffer solutions as well. The data for 1-diazo-2-indanone gave the hydronium ion catalytic coefficient kH+ = 5.7 × 103 (mol/L)1 s1 and the isotope effect kH+/kD+ = 2.9. The normal direction (kH/kD > 1) of this isotope effect was taken as evidence for a reaction mechanism involving rate-determining hydron transfer from the hydronium ion to the substrate's diazo carbon atom; followed by rapid displacement of diazo nitrogen by a water molecule, giving the observed 1-hydroxy-2-indanone product. The data for 2-diazo-1-indanone, on the other hand, gave a hydronium ion catalytic coefficient two orders of magnitude greater than the value for 1-diazo-2-indanone (kH+ = 5.9 × 101 (mol/L)1 s1), and an isotope effect near unity (kH+/kD+ = 1.2). It is argued that this isotope effect represents a situation in which diazo carbon hydronation and displacement of diazo nitrogen are each partly rate determining, a conclusion supported by incipient saturation of buffer catalysis in the formic acid buffer solutions. The 100-fold difference in hydronium ion catalytic coefficients for the two substrates is rationalized in terms of differing electron densities on the diazo carbon atoms.Key words: diazo compound hydrolysis, solution kinetics, acid catalysis, solvent isotope effects, buffer catalysis saturation.
The remarkable effect of 7-amino substituents on the reactivity of 4-nitrobenzofurazans with nucleophiles
Authors: Crampton Michael R , Isanbor Chukwuemeka , Willett Thomas C
Published: January 2006

The reactions of four 4-nitrobenzofurazans (4a4d) substituted at the 7 position with (a) N-ethyl, (b) N-butyl, (c) piperidino, or (d) pyrrolidino groups have been examined with sulfite ions and with hydroxide ions in waterDMSO (80:20, v/v). Addition of sulfite at the 5 position gives σ adducts with equilibrium constants ca. 105lower than that for the formation of the corresponding adduct from 4-nitrobenzofurazan. These reductions are attributed to the stabilization of the parent molecules 4a4d by conjugative interaction between the 4 and 7 substituents. In alkaline solution, 4a and 4b yield the conjugate bases while 4c and 4d suffer nucleophilic substitution to give 7-hydroxy-4-nitrobenzofurazan. Reactivity here is relatively high because of the iminium ion character of the substrates. Key words: benzofurazans, σ adducts, nucleophilic reactivity, substitution.
The fragmentation of 7-norbornyloxychlorocarbene  SNi-like transition states
Authors: Moss Robert A , Fu Xiaolin , Sauers Ronald R
Published: January 2006

7-Norbornyloxychlorocarbene (15) fragments mainly to 7-norbornyl chloride (16). A C-2 deuterated analog of 15 (syn-15-d) fragments to labeled chloride 16 with 78% retention and 22% inversion. When the deuterium label is replaced by a syn-exo-2-methyl group, the resultant carbene 22 fragments to syn- and anti-7-chloro-exo-2-methylnorbornane in a ratio of 1:1.1, corresponding to 48% retention and 52% inversion. Computational studies suggest that the fragmentations proceed via competitive SNi-like transition states that lead to either retention or inversion. Key words: carbenes, carbocations, SNi reactions, stereochemistry.
Ambident reactivity of phenoxyl radicals in DNA adduction
Authors: Manderville Richard A
Published: January 2006

Phenols are a class of compounds that can create beneficial effects in vivo owing to their antioxidant properties (through radical scavenging), or they can display hazardous effects owing to their pro-oxidant properties. The mechanism by which phenols act as pro-oxidants stems from their one-electron oxidation into reactive phenoxyl radicals by peroxidase enzymes or redox-active transition metals. In the presence of thiols and molecular oxygen, these reactive phenoxyl radicals stimulate an oxidative stress and cause oxidative damage to biomolecules, which is proposed to contribute to the occurrence of cancer in peroxidase rich tissues. Recent results from our laboratory show that certain phenoxyl radicals can also react directly with the C-8 site of deoxyguanosine to afford oxygen and carbon bonded adducts. This reactivity is consistent with the ambident (oxygen vs. C attachment) electrophilicity of phenoxyl radicals coupled with the susceptibility of the C-8 site of deoxyguanosine to radical attachment. Given that formation of covalent DNA adducts is regarded as the initiation event in the carcinogenic process, C-8 deoxyguanosine adducts of phenolic toxins are expected to contribute greatly to peroxidase driven toxic effects of phenolic xenobiotics. The focus of this review is the role of phenoxyl radicals in direct reactions with DNA and the use of Brown σ+ values to predict their reactivity.Key words: DNA adduction, phenoxyl radicals, chlorophenols, ochratoxin A, deoxyguanosine.
The aromatic character and resonance stabilization energies of substituted cyclopentadienyl and indenyl cations
Authors: Pincock J A , Speed A WH
Published: January 2006

Calculations (B3LYP/6-31G(d)) have been used to assess the aromaticity of 5-X substituted indenyl (4) and cyclopentadienyl (5) cations with X = O, NH2, OCH3, CH3, F, H, CN, and N2+. Two criteria were used, the aromatic stabilization energy (ASE), as determined by isodesmic reactions, and bond alternation, as determined from the Julg index (A) on the basis of carboncarbon bond lengths. Substituent effects on the singlet state of the cyclopentadienyl cations resulted in significant decreases in antiaromatic character for electron-donating groups as indicated by larger A values (A = 0.25 for X = H and +0.26 for X = NH2). These decreases paralleled increases in the C-2C-3 bond length and good linear correlations were obtained between A vs. the C-2C-3 bond length and A vs. the ASE. These effects were rationalized by the stabilization by the electron-donating groups of the positive charge at C-5 generated as a consequence of a JahnTeller distortion leading to a lowest energy singlet state with a HOMO of a2 symmetry. In contrast, the lowest energy triplet state for each of the substituted cyclopentadienyl cations has little bond alternation (A > 0.9) and, by this criterion, is not significantly antiaromatic. The triplet state is more stable than the singlet state for the unsubstituted case and those with electron-withdrawing groups (ΔEST = 11.3 and 9.3 kcal/mol for X = H and CN, respectively) (1 cal = 4.184 J), but less stable for electron-donating groups (ΔEST = +15.0 kcal/mol for X = NH2). For the indenyl cations 4, the ASE values were almost independent of the substituent and the A values only decreased slightly for electron-donating groups. The A values also indicated that the indenyl cations could be divided into two moieties, an X-substituted pentadienyl cation with considerable delocalization and little bond alternation, and a 2,3-butadiene one with considerable bond alternation. This separation also placed the major portion of the positive charge on the pentadienyl part. The lack of symmetry in the substituted indenyl cations rationalizes the selective reactivity of the 5-methoxy-substituted cation at C-1. Finally, the resonance stabilization energies (RSE) of the substituted cations gave a linear correlation with the RSEs of 4-substituted benzylic cations.Key words: indenyl cations, cyclopentadienyl cations, substituent effects, stabilization energies.
A comparison of the mechanisms of hydrolysis of benzimidates, esters, and amides in sulfuric acid media
Authors: Cox Robin A
Published: January 2006

The mechanisms given in textbooks for both ester and amide hydrolysis in acid media are in need of revision. To illustrate this, benzimidates were chosen as model compounds for oxygen protonated benzamides. In aqueous sulfuric acid media they hydrolyze either by a mechanism involving attack of two water molecules at the carbonyl carbon to give a neutral tetrahedral intermediate directly, as in ester hydrolysis, or by an SN2 attack of two water molecules at the alkyl group of the alkoxy oxygen to form the corresponding amide, or by both mechanisms, depending on the structure of the benzimidate. The major line of evidence leading to these conclusions is the behavior of the excess acidity plots resulting from the rate constants obtained for the hydrolyses as functions of acid concentration and temperature. The first of these mechanisms is in fact very similar to one found for the hydrolysis of benzamides, as inferred from: (1) similar excess acidity plot behaviour; and (2) the observed solvent isotope effects for amide hydrolysis, which are fully consistent with the involvement of two water molecules, but not with one or with three (or more). This mechanism starts out as essentially the same one as that found for ester hydrolysis under the same conditions. Differences arise because the neutral tetrahedral intermediate, formed directly as a result of the protonated substrate being attacked by two water molecules (not one), possesses an easily protonated nitrogen in the amide and benzimidate cases, explaining both the lack of 18O exchange observed for amide hydrolysis and the irreversibility of the reaction. Protonated tetrahedral intermediates are too unstable to exist in the reaction media; in fact, protonation of an sp3 hybridized oxygen to put a full positive charge on it is extremely difficult. (This means that individual protonated alcohol or ether species are unlikely to exist in these media either.) Thus, the reaction of the intermediate going to product or exchanged reactant is a general-acid-catalyzed process for esters. For amide hydrolysis, the situation is complicated by the fact that another, different, mechanism takes over in more strongly acidic media, according to the excess acidity plots. Some possibilities for this are given.Key words: esters, amides, benzimidates, hydrolysis, excess acidity, mechanism, acid media.
Deuterium labeling as a test of intramolecular hydride mechanisms in the fragmentation of 2-(1-hydroxybenzyl)-N1′-methylthiamin
Authors: Ikeda Glenn , Kluger Ronald
Published: January 2006

2-(1-Hydroxybenzyl)-N1′-methylthiamin (1b) is a model for the addition intermediate in the thiamin catalyzed benzoin condensation. However, N-alkylation alters the reactivity of the compound: instead of undergoing base-catalyzed formation of benzaldehyde and N1′-methylthiamin, it rapidly forms trimethyl amino pyrimidine (2b) and phenylthiazole ketone (3). The base-catalyzed fragmentation process is faster than the analogous enzymic reaction (in benzoylformate decarboxylase) under the same conditions. One possible mechanism for the rapid fragmentation is an internal hydride transfer from α-C2 to the methylene bridge between the heterocycles. To test the hydride mechanism we prepared α-C2-deuterated 1b and conducted the fragmentation reaction in normal water. Spectroscopic analysis revealed that the trimethyl aminopyrimidine product does not contain any deuterium, ruling out a hydride transfer mechanism. This supports a mechanism for fragmentation that proceeds instead via a proton transfer from α-C2. Since protonation (and hence, deprotonation) of that site is part of the normal catalytic cycle of benzoylformate decarboxylase, the enzyme must divert the reaction from the lowest energy pathway since it would share a common intermediate with the fragmentation process.Key words: thiamin, fragmentation, benzoylformate decarboxylase, proton transfer, hydride shift.
Reactions of acetoxy(methylthio)carbene and S-methyl thiopyruvate
Authors: Klys Arkadiusz , Czardybon Wojciech , Warkentin John , Werstiuk Nick Henry
Published: January 2006

Thermolysis of 2-acetoxy-5,5-dimethyl-2-methylthio-Δ3-1,3,4-oxadiazoline in benzene at 110 °C afforded S-methyl 2-oxopropanethioate (S-methyl thiopyruvate) from 1,2-acyl migration in acetoxy(methylthio)carbene, as well as S,S-dimethyl 2-acetoxy-2-methylpropanebis(thioate) and S-methyl 2-acetoxy-2-(methylthio)butanethioate. The latter two, both composed of two carbene units, are derived from reaction of the first product with the carbene.Key words: acetoxy(methylthio)carbene, carbene, S-methyl thiopyruvate, rearrangement.
Formation and stability of organic zwitterions  The carbon acid pKas of the trimethylsulfonium and tetramethylphosphonium cations in water
Authors: Rios Ana , O'Donoghue AnnMarie C , Amyes Tina L , Richard John P
Published: January 2006

We report second-order rate constants of kDO = 7.5 × 104 and 9.9 × 105 (mol/L)1 s1 for exchange for deuterium of the first methyl proton of the trimethylsulfonium and tetramethylphosphonium cations, respectively, in D2O at 25 °C and I = 1.0 (KCl). The data were analyzed to give the following carbon acidities for these cationic carbon acids in water: (CH3)3S+, pKa = 28.5; (CH3)4P+, pKa = 29.4. These acidities are close to those of the neutral carbon acids acetonitrile and dimethylacetamide. This provides evidence that a portion of the stabilization of the cyanomethyl carbanion is due to resonance delocalization of negative charge from carbon to cyano nitrogen.Key words: carbon acids, carbanions, ylides, proton transfer.
A temperature-annealing effect on the hostguest complexation with γ-cyclodextrin
Authors: Wright P John , Bohne Cornelia
Published: January 2006

Pyrene binds to γ-cyclodextrin and forms hostguest complexes with different stoichiometries. The fluorescence of pyrene was employed as a qualitative signature for these different complexes. Solutions prepared at room temperature were shown not to be in thermodynamic equilibrium, since a heating cycle of 20 min at 80 °C followed by cooling led to changes in the relative concentrations of the pyreneγ-cyclodextrin complexes. This temperature-annealing effect has consequences when determining thermodynamic parameters such as equilibrium constants and hostguest stoichiometries. Key words: cyclodextrin, pyrene, aggregates, fluorescence.
On the displacement reactions of organic substances in water
Authors: Scott J MW
Published: January 2006

The hydrolyses of a series of organic halides, nitrates, sulphonates, and perchlorates are examined from the standpoint of thermodynamics, kinetics, temperature dependence, isotope effects, the Kurz equation, and the Guthrie linear free energy relationship. The thermodynamics of several definite bimolecular displacements are also examined. Some mechanistic revisions are suggested to reach an improved accommodation with the experimental observations.Key words: kinetics, thermodynamics, hydrolytic displacements, mechanism, ionic displacements, nucleofugality, linear free energy relationships.
The kinetics of the spontaneous, proton- and AlIII-catalysed hydrolysis of 1,5-anhydrocellobiitol  Models for cellulose depolymerization in paper aging and alkaline pulping, and a benchmark for cellulase efficiency
Authors: Baty John William , Sinnott Michael L
Published: January 2006

The kinetics of the spontaneous, proton- and AlIII-catalysed hydrolyses of the C1O4′ bond in 1,5-anhydrocellobiitol have been measured at elevated temperatures (125.0220.0 °C). Data for the first two processes extrapolate to the expression k = (8.6 ± 2.1 × 1016) + (1.4 ± 0.2 × 109-pH) s1 at 25 °C. These room-temperature figures were used to model cellulose depolymerization by the af Ekenstam equation. The spontaneous process is too slow to contribute to loss of paper strength on aging, and even the acid-catalysed process is significant only below ~pH 4.0. However, the spontaneous hydrolysis readily accounts for the reduction of cellulose degree of polymerization (DP) during alkaline (e.g., kraft) pulping of cellulose fibres. Efficient electrophilic catalysis by AlIII was observed at 150.0 °C in 0.1 mol/L succinate buffers of room temperature pH 3.05 and 3.35 (k2 = 8.1 ± 0.4 × 103 and 4.2 ± 0.2 × 103 (mol/L) 1 s1, respectively). The apparent activation energy of the AlIII-catalysed process was 31 ± 4 kJ mol-1, lower than that of the proton-catalysed path, suggesting the electrophilic catalysis increases in importance as the temperature approaches ambient. Consequently, it appears that the culprit in the impermanence of “rosin-alum” -sized paper is AlIII, directly acting as a Lewis acid, not the AlIII hydration sphere as a Brønsted acid. Conservation measures should either address this or be generic (e.g., low-temperature storage). Key words: cellulose, hydrolysis, kraft pulping, paper conservation, rosin-alum sizing.
Influence of the number of water molecules on the mechanism of N-sulfinylaniline hydrolysis
Authors: Ivanova Elena V , Muchall Heidi M
Published: January 2006

The mechanism of the uncatalyzed hydrolysis of N-sulfinylaniline (Ph-N=S=O) has been studied with B3LYP/6-31+G(2d,2p) in the gas phase, with explicit treatment of water molecules. Hydrolysis involves water attack on sulfur, with a close to perpendicular alignment of a water molecule and the NSO plane in both prereaction complexes and transition states for the rate-determining step. Consequently, the distance of the weak S···O interaction, together with the efficiency of protonation of either nitrogen (attack across the N=S bond) or oxygen (attack across the S=O bond) atoms of the NSO group, determines the height of the activation barrier for hydrolysis. While the reaction with one water molecule is characterized by an unreasonably high enthalpy of activation, a cooperative effect from the weak interactions appears with the inclusion of a second water molecule, where both participate in the reaction, and the activation enthalpy drops significantly. The preference for attack across the S=O bond that is found in the reaction with one water molecule switches to a dominance of attack across the N=S bond in the reaction with three water molecules.Key words: N-sulfinylaniline, hydrolysis, mechanism, density functional theory (DFT).
Intramolecular general acid catalysis of sulfate transfer  Nucleophilic attack by oxyanions on the SO3 group
Authors: Kirby Anthony J , Gesser José Carlos , Hollfelder Florian , Priebe Jacks P , Nome Faruk
Published: January 2006

The mechanism of hydrolysis of 8-N,N-dimethylaminonaphthyl sulfate closely resembles that of the corresponding phosphate monoester. Nucleophilic attack by water on the sulfate group of the zwitterion is catalyzed by the neighbouring dimethylammonium group, acting as a particularly efficient general acid through the intramolecular hydrogen bond. This hydrogen bond is present in both reactant and product, but is strongest in the transition state. Transfer of the sulfuryl group to oxygen nucleophiles, including water and carboxylate anions, shows steric and electrostatic effects, and a sensitivity to basicity which is low, but significantly higher than expected for uncatalyzed transfer of the SO3 group.Key words: sulfate, sulfatase, intramolecular, general acid catalysis, promiscuity.
Dissociation of the phenanthroimidazole dimer  A highly delocalized radical  Gomberg revisited
Authors: Kiepek Eric , Zhou Yuhui , Hoz Shmaryahu , Rozental Ester , Kazmaier Peter M , Buncel Erwin
Published: January 2006

Results of a calculational study at the B3LYP/6-3/G* level concerning the dimerization of the phenanthroimidazole radical are reported herein. The optimized minimum energies of six dimer structures corresponding to CC, CN, and NN bonding have been obtained. The lowest energy dimer is found to be that resulting from NN bonding (12). However, this does not correspond to an X-ray structure study of the experimentally isolated dimer (13), which reveals CN bonding, as is also deduced from an NMR investigation. The variance between the experimental structure and the calculational lowest energy one is examined on the basis of steric interactions: virtually retained planarity, and hence, full conjugation in the two phenanthroimidazole halves in 12, vs. twisting and lack of coplanarity in the other dimer structures. Importantly, spin density calculations reveal a negligible spin density on the nitrogens, rendering dimer 12 formation through NN bonding highly improbable. A bond dissociation energy of 16.5 kcal/mol (1 cal = 4.184 J) is calculated for the experimental dimer 13, which is by far the lowest CN bond energy recorded so far in the literature. As well, this value is of the same order of magnitude as the calculated CC BDE in hexaphenylethane, which had been postulated by Gomberg in 1900 as the molecule formed on dimerization of the triphenymethyl radical, but so far not observed experimentally. Key words: delocalized radical dimerization, phenanthroimidazole dimer, Gomberg's dimer, X-ray structure, CN bond dissociation energy.
Effective and regioselective iodination of arenes using iron(III) nitrate in the presence of tungstophosphoric acid
Authors: Jafarzadeh Mohammad , Amani Kamal , Nikpour Farzad
Published: January 2006

An easy, cheap, and effective method for iodination of various aromatic compounds takes place with molecular iodine and iron nitrate nonahydrate as the oxidant in the presence of a catalytic amount of tungstophosphoric acid in dichloromethane, with good yield and high regioselectivity under very mild conditions.Key words: iodination, arenes, iodine, iron(III) nitrate, tungstophosphoric acid.
Adventive-root development in mature black spruce and balsam fir in the boreal forests of Quebec, Canada
Authors: Krause C , Morin H
Published: January 2006

Black spruce (Picea mariana (Mill.) BSP) and balsam fir (Abies balsamea (L.) Mill.) are the two main tree species in the boreal forests of Quebec, Canada, and both show adventive-root formation. Little is known about the dynamics of adventive-root initiation and the pattern of length growth. To gain a better understanding of root growth, the root systems of 30 mature black spruce and 30 mature balsam fir were excavated until the root diameter had decreased to 2 cm. Tree ages ranged from 100 to more than 250 years. All trees showed only adventive roots; this was confirmed by dating the rootshoot interface. The youngest lateral roots were located close to ground level, whereas the oldest ones occurred lower in the stump, suggesting a process of renewal for the latter. Reconstruction of the development of the root system revealed a specific root-growth pattern. Adventive roots grew, on average, more than 60% of their total length in the year of initiation, whereas more than 93% of lateral-root elongation was recorded in the first 10 years after adventive roots were initiated. This growth pattern was found to be similar in the two tree species in terms of lateral-root development (p = 0.68). More variability was observed for the ramified adventive roots. However, two patterns emerged. First, around 10% of total elongation was completed in the same year as that of the corresponding lateral roots. Second, several ramified adventive roots were initiated in the same calendar year but delayed by several years relative to lateral adventive root initiation. No significant differences were observed between black spruce and balsam fir (p = 0.1).
Wood ash as a fertilizer on drained mires  growth and foliar nutrients of Scots pine
Authors: Moilanen Mikko , Silfverberg Klaus , Hökkä Hannu , Issakainen Jorma
Published: January 2006

The availability of phosphorus (P) and potassium (K) commonly limits tree growth on drained peatlands. The nutritional status and volume growth of Scots pine (Pinus sylvestris L.) after varying doses of wood ash fertilization were investigated in seven field experiments located on deep-peated sites in Finland between latitudes 63°N and 67°N. Needle samples were taken 1420 years after fertilization and trees measured 15 years after fertilization. Annual growth rates and differences in foliar nutrients were analyzed with a two-way ANOVA model. A regression model was used in the analysis of periodic relative volume growth. High doses of wood ash (100265 kg P·ha1, 225450 kg K·ha1) resulted in greater changes in foliar nutrient concentrations and in a stronger growth response than low doses (550 kg P·ha1, 14210 kg K·ha1). Significant increases in needle mass and concentrations of P, K, and B were observed in the ash-fertilized stands, with a good status for these elements 20 years after fertilization. Depending on the ash dose, the mean annual volume growth was 0.51.4 m3·ha1 higher than in the control plots during the 15 year postfertilization period.
The effect of soil temperature and light on sprouting and rooting of root cuttings of hybrid aspen clones
Authors: Stenvall N , Haapala T , Aarlahti S , Pulkkinen P
Published: January 2006

Root cuttings from five clones of hybrid aspen (Populus tremula L. × Populus tremuloides Michx.) obtained from 2-year-old stock plants were grown in a peatsand mixture (soil) at four soil temperatures (18, 22, 26, and 30 °C). Half of the cuttings were grown in light and the rest in darkness. The root cuttings that were grown at the highest soil temperature sprouted and rooted significantly better than the cuttings grown at the lower temperatures. Light did not affect the sprouting of root cuttings but did have a negative effect on their rooting. Moreover, the clones varied significantly in sprouting and rooting percentages, as well as in the time required for sprouting. In general, higher soil temperatures hastened sprouting of the cuttings. Sprouting was also faster in the light than in the dark treatment. Differences in soil temperature, light conditions, or clone had no significant effect on rooting time.
Heartwood extractives in larch and effects on X-ray densitometry
Authors: Grabner Michael , Wimmer Rupert , Gierlinger Notburga , Evans Robert , Downes Geoff
Published: January 2006

The genus Larix is exceptional for its high content of extractives in the heartwood, with the dominating component arabinogalactan found abundantly in cell lumens of tracheids. On samples prepared from 100 European larch (Larix decidua Mill.) and hybrid larch (L. decidua × Larix kaempferi (Lamb.) Carr.) trees, extractive contents and wood density were measured using X-ray densitometry. A strong relationship between the amount of hot water extractives and the loss of density owing to the extraction process was found. Prior to extraction, increasing extractive content went hand-in-hand with higher wood density. At the heartwoodsapwood boundary, the density level dropped. After acetone and hot water extraction, the drop was no longer visible. Without proper consideration of the extractives in larch growth sites, comparisons in wood quality studies looking at wood density differences may become faulty, breeding studies could lead to incorrect selection strategies, and tree-ring studies may not deliver the expected climatic signals. Hence, hot water extractions should take place prior to radiation exposure.
Is ring width a reliable proxy for stem-biomass increment? A case study in European beech
Authors: Bouriaud O , Bréda N , Dupouey J -L , Granier A
Published: January 2006

The relationship between basal-area increment and stem-volume increment or biomass annual production was investigated in 30 dominant European beech (Fagus sylvatica L.) in northeastern France. The trees were sampled at four heights along the stem for dendrochronological and densitometric measurements. Annual stem-volume and stem-biomass increments were computed from the measurements and were not obtained by applying allometric relationships. A comparison of the ring-area increments at the four stem heights indicated that the vertical distribution of annual growth fluctuates at an interannual time step and is influenced by climate during the growing season, particularly drought events. Ring-area increments were more strongly reduced at breast height than in the upper parts of the tree during dry years. Relationships between basal-area increment and volume or annual biomass production were very strong, but the residuals of these relationhips contained up to 50% climate information. The amplitude of the breast-height radial-growth response to drought is much larger than the volume and biomass-production responses. Variations of wood density in this diffuse-porous species are not large enough to consistently modify the estimates of annual stem biomass production. Breast-height series are a valuable tool for dendrochronological investigations, but as they are more sensitive to drought, they greatly underestimate tree biomass increments during drought episodes.
Patch structure, fire-scar formation, and tree regeneration in a large mixed-severity fire in the South Dakota Black Hills, USA
Authors: Lentile Leigh B , Smith Frederick W , Shepperd Wayne D
Published: January 2006

We compared patch structure, fire-scar formation, and seedling regeneration in patches of low, moderate, and high burn severity following the large (~34 000 ha) Jasper fire of 2000 that occurred in ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) forests of the Black Hills of South Dakota, USA. This fire created a patchy mosaic of effects, where 25% of the landscape burned as low, 48% as moderate, and 27% as high severity. Dead cambium on a significant portion of tree circumference in a tree with live cambium and a vigorous crown was taken as evidence of incipient fire-scar formation. Tree mortality was approximately 21%, 52%, and 100% in areas of low, moderate, and high burn severity, respectively. Dead cambium was detected on approximately 24% and 44% of surviving trees in low and moderate burn severity patches, respectively. Three years postfire, regeneration densities were ~612 and 450 seedlings·ha1 in low and moderate burn severity patches, respectively, and no regeneration was observed in the interior of high burn severity patches. Fire-scars will be found on 73% of the area burned in this fire, and large patches of multicohort forest will be created. Mixed-severity fire may have been common historically in the Black Hills, and in conjunction with frequent surface fire, played an important role in shaping a spatially heterogeneous, multicohort ponderosa pine forest.
Field efficiency and bias of snag inventory methods
Authors: Kenning Robert S , Ducey Mark J , Brissette John C , Gove Jeffrey H
Published: January 2006

Snags and cavity trees are important components of forests, but can be difficult to inventory precisely and are not always included in inventories because of limited resources. We tested the application of N-tree distance sampling as a time-saving snag sampling method and compared N-tree distance sampling to fixed-area sampling and modified horizontal line sampling in mixed pine-hardwood forests of southern Maine and New Hampshire. We also present a novel modification of N-tree distance sampling that limits the distance from plot center that an observer must search to find tally trees. A field test shows N-tree to be quick, but generally biased and characterized by high variability. Distance-limited N-tree sampling mitigates these problems, but not completely. We give recommendations for operational snag inventory in similar forest types.
Using multivariate factorial kriging for multiscale ordination: a case study
Authors: Nanos Nikos , Pardo Fernando , Nager Jesus Alonso , Pardos José Alberto , Gil Luis
Published: January 2006

Vegetation ordination is usually based on classical data reduction techniques such as principal components analysis, correspondence analysis, or multidimensional scaling. The usual methods do not account for multiscale correlations among species. In this paper, we use a geostatistical method, known as multivariate factorial kriging, for studying multiple-scale correlations. The case study was carried out in a mixed broadleaf forest of central Spain. Six tree species were included in the analysis. Data analysis included (i) experimental variogram calculation and modeling with the use of the linear model of coregionalization, (ii) principal components analysis, and (iii) cokriging. The results indicate that correlations among species are different depending on the spatial scale. We conclude that competition for light is the main factor controlling the spatial distribution of species at the plot-level scale of variation. At larger scales of variation, soil conditions and (or) human intervention are the key factors in determining the observed vegetation pattern. Based on the factor scores for the largest scale of variation, we conducted a cluster analysis to identify plots with similar characteristics. The resulting clusters have the remarkable property of being spatially continuous.
GROUND-STATE BARYON MASSES IN THE PERTURBATIVE CHIRAL QUARK MODEL
Authors: INOUE T. , LYUBOVITSKIJ V. E. , GUTSCHE TH. , FAESSLER AMAND
Published: January 2006

The mass differences of the flavor octet and decuplet ground-state baryons are studied in the perturbative chiral quark model. We present a way to understand the nontrivial spin- and flavor-dependent mass differences, whereby both pseudoscalar mesons and gluons play a significant role.