bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of taxonomic level on the performance of a predictive model for water quality assessment
Authors: Feio Maria J , Reynoldson Trefor B , Graça Manuel AS
Published: January 2006

Predictive models developed to assess water quality in the Mondego River basin (Portugal), based on the BEnthic Assessment of SedimenT (BEAST) model, were compared at three identifications levels: order, family, and genus (species) of macroinvertebrates. Fifty-five reference sites were originally selected for building the model, but this number was reduced to 51 (lowest level), 52 (family), and 53 (order), after the grouping procedures (CLUSTER, MDS, and SIMPER; Primer 5.2.6, Primer-E Ltd., Plymouth, UK). The discriminating variables (stepwise discriminant analysis) stream order, current velocity, pool quality, and substrate quality were common to the genus (species) and family models. Substrate quality was the only discriminating variable of the order model. The model performances, based on their ability to correctly predict reference site membership (complete MDS with jackknifed cross-validation), ranged from 78% (lowest level) to 81% (family and order levels). Twenty test sites were used to compare site assessments using each of the models. We concluded that the lowest-level model of identification provides the best evaluations of water quality assessment and performed well, that the family-level model reacted similarly and could be a good alternative for bioassessment programmes, and that a greater effort toward improving our knowledge of aquatic macroinvertebrates in Portugal is recommended as species are important in assessing water quality.
Effects of biotic assemblage, classification, and assessment method on bioassessment performance
Authors: Mazor Raphael D , Reynoldson Trefor B , Rosenberg David M , Resh Vincent H
Published: January 2006

Biomonitoring requires thorough evaluation of methods used to detect impairment. Using a data set of 202 reference sites and 66 test sites from the Fraser River, British Columbia, Canada, we analyzed the effects of assemblage (benthic macroinvertebrates and periphyton) and reference site classification (ecoregion, stream order, null models, and biotic groups) on two bioassessment methods (BEAST (BEnthic Assessment of SedimenT) and RIVPACS (River InVertebrate Prediction And Classification Scheme)). Although largely undisturbed, the Fraser River is affected in some areas by logging, mining, agriculture, pulp mill effluent, and urban land use. Overall performance was evaluated using the harmonic mean of precision, accuracy, and two measures of sensitivity. Invertebrates and periphyton were equally accurate and precise, but invertebrates were more sensitive. Biotic groups were the least accurate and precise classification, but also the most sensitive and had the greatest overall performance. BEAST was slightly less accurate and precise than RIVPACS, equally sensitive to simulated disturbance, and more sensitive to real disturbance. Assessments with higher sensitivity frequently had lower accuracy, indicating a possible trade-off among these aspects of performance.
Fish predation and trapping for rusty crayfish (Orconectes rusticus) control: a whole-lake experiment
Authors: Hein Catherine L , Roth Brian M , Ives Anthony R , Zanden M Jake Vander
Published: January 2006

Improved methods are needed for the prevention and control of invasive species. We investigated the potential to control a rusty crayfish (Orconectes rusticus) population in an isolated lake in northern Wisconsin by trapping adult crayfish and restricting fishing, thereby increasing fish populations and predation on small crayfish. Over a 3 year period, traps and predatory fishes removed substantial portions of the rusty crayfish population. We used an age-structured population model to determine which removal method had the largest effect on crayfish population growth rates. Because more crayfish were vulnerable to and removed by fish predation than by trapping, fish predation caused a larger decline in the population growth rate. However, trapping removed crayfish with the highest reproductive value and caused the largest decline in population growth rate per individual crayfish removed. Consideration of density-dependent responses to removal is necessary to predict long-term effects on rusty crayfish population dynamics. Nonetheless, our results suggest that the combination of trapping and fish predation can control established rusty crayfish populations and deserves further consideration for management.
Non-Darcy Couette flow through a porous medium of magnetohydro-dynamic visco-elastic fluid with heat and mass transfer
Authors: Eldabe Nabil TM , Sallam S N
Published: January 2006

We analyze the steady magnetohydrodynamic flow of an incompressible electrically conducting visco-elastic fluid through a porous medium between two porous parallel plates under the influence of a transverse magnetic field. We obtain an exact solution for the BrinkmanForchheimer extension of Darcy's momentum equation for flow. We solve the equations of motion with a perturbation technique under the assumption that the Forchheimer number Fs = bν/u0 is small. We analyze heat and mass transfer in porous media. We obtain the skin friction τw, the Nusselt number Nu, and the Sherwood number Sh. Our numerical results show the effects of the physical parameters of our problem on the fluid flow as well as on the heat and mass transfer, on the skin friction, and on the rates of heat and mass transfer. PACS No.: 47.65.+a
Pion production and multifractality in ultrarelativistic nuclear collision  evidence of constant specific heat
Authors: Ghosh D , Deb A , Lahiri M B , Das R
Published: January 2006

Multifractal analysis of the pions produced in 32SAgBr and 16OAgBr interactions at 200 and 60 AGeV, respectively, is performed following the method proposed by Takagi. The generalized fractal dimensions Dq's are determined and found to decrease with order, thereby supporting multifractality in multiparticle production. From the knowledge of Dq, the multifractal specific heat is calculated for each interaction. It has been observed that the value of the specific heat is independent of the collision energy. PACS Nos.: 25.75q, 24.60.Ky, 12.40.Ee
D.C. electrical and optical properties of vacuum-deposited organic semiconductor FePcCl thin films
Authors: Rajesh K R , Menon C S
Published: January 2006

Sandwich and planar structures are fabricated by a vacuum deposition method using iron phthalocyanine chloride (FePcCl) as an active layer and gold (Au) as electrodes. The permittivity ε of FePcCl is determined from the dependence of capacitance on film thickness. The current density  voltage characteristics characteristics of the Au/FePcCl/Au structure at room temperature are found. Thermally generated hole concentration p0, hole mobility µp, total trap concentration Nt, and depth of the trap level are estimated. The activation energies of FePcCl films are determined from Arrhenious plots of ln σ versus 1000/T. The absorption and reflectance spectra of a FePcCl thin film deposited at room temperature are recorded in the spectral range 300900 nm. The optical band gap of a FePcCl thin film is determined from the α2 versus hν graph. The optical constants n and k are found. The real and imaginary parts of the optical dielectric constant ε1 and ε2 are calculated. These optical parameters are plotted against photonenergy. PACS Nos.: 72.80.Le, 73., 78.20.e
Extreme-ultraviolet wavelength and lifetime measurements in highly ionized krypton
Authors: Kukla K W , Livingston A E , Vogel Vogt C M , Berry H G , Dunford R W , Curtis L J , Cheng S
Published: January 2006

We have studied the spectrum of highly ionized krypton in the extreme-ultraviolet wavelength region (50300 Å), using beam-foil excitation of fast krypton ions at the Argonne ATLAS accelerator facility. We report measurements of transition wavelengths and excited-state lifetimes for n = 2 states in the lithiumlike, berylliumlike, and boronlike ions, Kr31+,32+,33+. Excited state lifetimes ranging from 10 ps to 3 ns were measured by acquiring time-of-flight-delayed spectra with a position-sensitive multichannel detector.PACS Nos.: 32.70.Cs, 32.30.Jc, 34.50.Fa
Circular footings on a cemented layer above weak foundation soil
Authors: Thomé Antônio , Donato Maciel , Consoli Nilo Cesar , Graham James
Published: January 2006

This work proposes a method for predicting the behavior of shallow footings bearing on an upper layer of processed cemented soil that overlies a lower layer of weakly bonded residual soil with a high void ratio. The paper describes the results of a series of field plate tests and numerical simulations. The results lead to a semi-empirical method for designing shallow foundations on a double-layer system. The method has been validated by comparison of predicted values with results from a separate series of plate-loading tests. For engineering practice, the proposed method provides acceptable predictions of bearing capacities and loadsettlement curves.Key words: footings, cemented layer, layered system, weakly bonded, high void ratio.
Behavior of gravity deposited granular material under different stress paths
Authors: Ng Tang-Tat
Published: January 2006

The behavior of granular material with different densities subjected to various stress paths was investigated by numerical modeling. The simulated samples consisted of two different kinds of ellipsoids. The ellipsoids were mixed in the proportions 50:50 by weight. The longer particles have an aspect ratio (major length/minor length) of 1.5, and the other particles have an aspect ratio of 1.2. The numerical experiments were conducted with the discrete element method. Three samples of different densities were simulated by deposition under gravity to mimic the air pluviation method. They were then consolidated isotropically. Eleven stress path triaxial tests were simulated for each sample. The strength and deformational behaviors of these samples are presented. The effects of density and stress path are examined.Key words: shear strength, granular material, soil mechanics, stress path, stress-strain curve.
Influence of rainfall regime on hydraulic conditions and movement rates in the overconsolidated clayey slope of the Orvieto hill (central Italy)
Authors: Tommasi Paolo , Pellegrini Paola , Boldini Daniela , Ribacchi Renato
Published: January 2006

The medieval town of Orvieto is built on the top of a pyroclastic slab overlying a gentle slope of overconsolidated clays. The clayey slope has been constantly affected by landslide phenomena in the form of slow movements and failure events, which in turn have periodically caused instability of the marginal areas of the pyroclastic slab. Since 1982 a number of Casagrande-type piezometers and inclinometers were installed in the northern slope of the Orvieto hill within the area that was involved in the huge Porta Cassia landslide in 1900. In this paper, after a brief description of the geology and the geotechnical properties of the slope, data obtained through the monitoring system are illustrated. Piezometric data are utilized to develop a conceptual model of the hydraulic conditions in the clayey slope, and inclinometer measurements are interpreted and correlated with the geotechnical ground profile and slope morphology to understand the present complex evolution of the clayey slope. Finally, the strong correlation among the rainfall regime, the piezometric levels, and the rate of movements is discussed, and the recurrence periods of critical cumulative rainfall on displacement trends are estimated on the basis of statistical methods.Key words: overconsolidated clays, slope movements, piezometric levels, rainfall.
Evaluation of the predictive ability of two elastic-viscoplastic constitutive models
Authors: Hinchberger Sean D , Rowe R Kerry
Published: January 2006

Two elastic-viscoplastic constitutive formulations are evaluated using laboratory and field data from Sackville, New Brunswick and Gloucester, Ontario. Both constitutive models have been implemented in a finite element program and formulated for undrained analysis and fully coupled analysis based on Biot consolidation theory. A laboratory study of the rate-sensitive behaviour of Sackville clay is described. The response of Sackville clay during consolidated anisotropic undrained (CAU) triaxial creep, CAU triaxial compression, and incremental oedometer consolidation is compared with the calculated behaviour. The comparisons demonstrate the general ability of three-parameter elastic-viscoplastic constitutive models to satisfactorily describe the rate-dependent behaviour of Sackville clay. The measured response of Gloucester clay during long-term Rowe cell consolidation tests is compared with the calculated behaviour, and the predictive ability of both constitutive formulations is evaluated using the field performance of the Gloucester case record. In undertaking the present study, the predictive ability of two elastic-viscoplastic constitutive models is examined for two soft clays. A new method of overstress measurement is introduced for elliptical yield surfaces and the importance of adopting a scalable yield surface for the constitutive modeling of soft clay is demonstrated. A model that is suitable for the study of reinforced and unreinforced embankments on soft rate-sensitive clay foundations is identified.Key words: elastic-viscoplastic, finite element analysis, overstress viscoplasticity, case study, rate-sensitive, coupled analysis.
The epsilon method: analysis of seepage beneath an impervious dam with sheet pile on a layered soil
Authors: Feng Zheng-yi , Wu Jonathan TH
Published: January 2006

An approximate solution method, referred to as the epsilon method, allows flow characteristics such as flow rate and exit gradient to be determined for seepage through a two-layer soil system. The finite element program SEEP was employed to analyze flow characteristics of an impervious dam with sheet pile on a layered soil. Extensive analyses were performed for different conditions, including soil layer thickness, soil hydraulic conductivity, dam width, and sheet pile depth. The flow rate and exit gradient were determined for each condition analyzed. The results were reduced to simple charts, called the epsilon curves. The epsilon curves allow a designer to obtain solutions to the seepage problem without a computer code and to verify solutions obtained from a computer code. They are especially useful when searching for an optimum design of a masonry dam. The epsilon curves can be extended to a soil system comprising more than two layers. An example of a single-row sheet pile structure in a three-layer system is given to illustrate how to use the method for multiple-layer systems. The method was verified by comparing the results with those obtained from the SEEP program, and excellent agreement was noted.Key words: seepage, dam, sheet pile, layered soil, hydraulic conductivity.
Representativeness of measurements in the interpretation of earth dam behaviour
Authors: Pagano Luca , Sica Stefania , Desideri Augusto
Published: January 2006

The representativeness of measurements monitored in earth dams is analysed to investigate how a given measured quantity can be used to interpret the dam's mechanical behaviour. Representativeness is evaluated on the basis of spatial continuity of the measured quantity and the sensitivity of that quantity to natural mechanical nonhomogeneity. The discussion is supported by results from case studies and numerical examples. The study is mainly focused on pore-water pressure measurements. Spatial continuity of pore-water pressure is analysed with consideration of both saturation and drainage conditions. The paper discusses how pore-water pressure representativeness can vary over the lifetime of the dam.Key words: earth dam, pore-water pressure, monitoring.
Solvolysis and ring closure of quinone methides photogenerated from biaryl systems
Authors: Shi Yijian , Wan Peter
Published: January 2006

A variety of biaryl quinone methides have been photogenerated with a range of efficiencies from biaryl precursors 46 and 8, 10, and 11, all having hydroxyl and hydroxymethyl substituents on alternate rings. These novel biaryl quinone methides, which cannot be readily generated via thermal chemistry, are trapped by added nucleophiles such as MeOH and ethanolamine; two that cannot undergo electrocyclic ring closure (from 8 and 11) are readily observable by nanosecond laser photolysis, with long wavelength maxima (λmax) of 600 and 520 nm, respectively. Photogenerated o,o′-biaryl quinone methides undergo electrocyclic ring closure to give the corresponding chromene (pyran) products in high yield. Since the precursor biaryl alcohols have highly twisted structures in the ground state (dihedral angle of up to 90° by molecular mechanics calculations), a significant twisting motion to planarity is required to achieve reaction. Using steady-state fluorescence studies, we present evidence to suggest that the mechanism of quinone methide formation may occur via one of the following mechanisms: (i) dissociation of the proton from ArOH that precedes twisting; or (ii) ArOH dissociation and twisting taking place either simultaneously or in quick succession.Key words: biaryl quinone methide, photosolvolysis, photodeprotonation, photocyclization.
An ab initio study of 1,5-suprafacial shifts in 5-substituted 1,3-cyclopentadienes
Authors: Pye Cory C , Poirier Raymond A
Published: January 2006

A computational study of the degenerate 1,5-suprafacial migration of the 5-substituted cyclopentadienes is presented. The substituents considered are the Group 1417 elements of the second through fifth periods, saturated by hydrogens as needed to fulfill normal valence requirements. The geometry of most transition states are remarkably similar in the carbon framework. The activation barrier to migration was shown to correlate well with a dimensionless "stretching" parameter, especially at the MP2 level.Key words: 5-substituted 1,3-cyclopentadiene, 1,2-haptotropic shift, 1,5-suprafacial shift, ab initio, transition states.
Hydrolysis of aryl hydrogen maleate esters mediated by cyclodextrins  Effect on the intramolecular catalysis
Authors: Andrés Gabriel O , Silva O Fernando , de Rossi Rita H
Published: January 2006

Kinetic studies of the hydrolysis of Z-aryl hydrogen maleates (Z = H, p-CH3, m-CH3, p-Cl, m-Cl) were carried out in the presence and absence of hydroxypropyl-β-cyclodextrin (HPCD) at variable pH from 1.00 to 3.00. The reaction involves the formation of maleic anhydride as an intermediate and the rate of its formation is strongly dependent on the pH. This is because the neighboring carboxylate group is a better catalyst than the carboxylic group. The rate constant for the formation of maleic anhydride decreases as the HPCD concentration increases in a nonlinear fashion. The results were interpreted in terms of the formation of a 1:1 inclusion complex of the esters with HPCD. The neutral (HA) and anionic (A) species of the substrate have different association constants (K[Formula: see text] and K[Formula: see text]). In all cases studied,

K[Formula: see text] is higher than K[Formula: see text] for the same substrate. This difference is responsible for a decrease in the amount of the anionic substrate (reactive species) in the presence of HPCD, which results in a diminution of the observed rate constant. Besides, the rate constant for the reaction of the complexed substrate is smaller than that in the bulk solution indicating that the transition state of the cyclodextrin mediated reaction is less stabilized than the anionic substrate. The values of ΔΔGare almost independent of the substituent on the aryl ring and range within 0.48 and 1.05 kcal mol1(1 cal = 4.184 J). There is no correlation between KTSand the association constant of the substrate indicating that the factors stabilizing the transition state are different from those that stabilize the substrate. Key words: cyclodextrins, intramolecular catalysis, hydrolysis, inhibition.
Photochemistry of 9-methylbicyclo[3.3.1]nonyl aryl ketones  A novel 1,5-disproportionation of 1,4-hydroxy biradicals and asymmetric induction using the solid-state ionic chiral auxiliary method
Authors: Chen Shuang , Patrick Brian O , Scheffer John R
Published: January 2006

A novel 1,5-disproportionation reaction has been discovered for 1,4-hydroxy biradicals derived from the photolysis of 9-methylbicyclo[3.3.1]nonyl phenyl ketones (1), which undergo mainly Yang cyclization both in solution and the solid state. By applying the solid-state ionic chiral auxiliary method of asymmetric synthesis to the Yang cyclization, enantiomeric excesses as high as 95% were achieved at high reaction conversions. The origin of the reaction selectivity is discussed with the help of X-ray crystallography. In addition, the solid-state photoreaction of ketone 1b was found to occur in a single crystal-to-single crystal fashion.Key words: photochemistry, 1,4-hydroxy biradical, disproportionation, asymmetric induction, ionic chiral auxiliary, single crystal-to-single crystal reaction.
Computational studies of the properties of phenyloxenium ions  A comparison with phenylnitrenium and phenylcarbenium ions
Authors: Glover Stephen A , Novak Michael
Published: January 2006

Properties of phenyloxenium ion 13a, phenylnitrenium ion 14a, and their 4-methyl and 4-phenyl analogues have been studied at the HF/6-31G* and pBP/DN*//HF/6-31G* levels to explain differences in their relative ease of formation and their stabilities. The phenyloxenium ions 13 are ground-state singlets but S0T1 gaps are smaller than those of the corresponding nitrenium ions. The S0 states are stabilized by donor methyl and phenyl substituents in both classes of ions, but phenyloxenium ion has much greater charge localization on the ring, primarily at the 4 position. Evidence for this difference stems from ground-state HF/6-31G*geometries, dipole moments, and vibrational frequencies. Nitrenium ions exhibit some quinoidal character, but the calculated CN bond lengths are longer than those of their 4-hydroxy-2,5-cyclohexadienone imine hydration products 17 and the symmetric C-N stretching frequencies are ca. 60100 cm1 less than those of 17. However, the CO bond lengths and stretching frequencies of the phenyloxenium ions are slightly shorter and greater, respectively, than those of their 4-hydroxy-2,5-cyclohexadienone hydration products (16). The oxenium ions are best described by their 4-oxo-2,5-cyclohexadienyl carbenium resonance structures. Accordingly, a 4-phenyl group stabilizes the phenyloxenium ion more than the phenylnitrenium ion leading to a planar geometry and considerably more charge in the distal ring, thus accounting for regioselectivities of azide reactions. Isodesmic comparisons of the energy difference between phenyloxenium and phenylnitrenium ions and their neutral hydration products explains their relative stabilities under aqueous conditions; whereas 4-biphenylyloxenium ion 13c has a lifetime in water of 12 ns as opposed to the corresponding nitrenium ion 14c (300 ns), the 4-methylphenyloxenium ion 13b is less stable to hydration by 18.7 kcal mol1 (1 cal = 4.184 J) and cannot be observed under the conditions used to generate 13c.Key words: oxenium ions, nitrenium ions, computational chemistry, nucleophilic addition, singlet state properties.
The HERON reaction  Origin, theoretical background, and prevalence
Authors: Glover Stephen A , Rauk Arvi , Buccigross Jeanne M , Campbell John J , Hammond Gerard P , Mo Guoning , Andrews Luke E , Gillson Ashley-Mae E
Published: January 2006

The origin of the HERON reaction is reviewed from a historical perspective and shown to have its foundation in the unusual properties of bisheteroatom-substituted amides, so-called anomeric amides. The reaction involves migration of anomerically destabilized oxo-substituents on an amide nitrogen to the amide carbon and dissociation of the amide bond. Computational work providing a theoretical basis for the reaction is presented, together with physical organic measurements that support results therefrom. The rearrangement has been observed in a number of chemical transformations of N-alkoxy-N-aminoamides, reactions of 1-acyloxy-1-alkoxydiazenes, N-alkoxy-N-aminocarbamates, N-alkoxyhydroxamic acids, as well as in the gas-phase reactions of N-acyloxy-N-alkoxyamides.Key words: HERON reaction, anomeric amides, rearrangements, hindered esters, concerted reactions.
Benzenesulfonyl chloride with primary and secondary amines in aqueous media  Unexpected high conversions to sulfonamides at high pH
Authors: King James F , Gill Manjinder S , Ciubotaru Petru
Published: January 2006

We have determined pHyield profiles under pseudo-first-order conditions of the reactions of benzenesulfonyl chloride with a set of primary and secondary water-soluble alkylamines, and have found with certain amines, such as dibutylamine, a profile taking the form of a sigmoid pH–yield curve with relatively high yields of the sulfonamide persisting with increasing basicity up to and including 1.0 mol/L sodium hydroxide. This behaviour is quantitatively accounted for by invoking, in addition to the usual second-order reaction of the sulfonyl chloride with the amine, two third-order terms (i) one first-order in sulfonyl chloride, amine and hydroxide anion, and (ii) another first-order in sulfonyl chloride and second-order in the amine. The importance of the third-order terms correlates approximately with the total number of alkyl carbon atoms in the amine, and this in turn is regarded as related to the hydrophobic character of the amine. Experiments to test this picture included: (i) observation of a bell-shaped curve with bis(2-methoxyethyl)amine, (ii) in the reaction of dibutylamine in THF–H2O (1:1), and also (iii) in the reaction of dibutylamine in 1.0 mol/L tetrabutylammonium bromide, and (iv) increase in the contributions of the third-order terms in 1.0 mol/L aqueous sodium chloride. Preparative reactions with dibutylamine, 1-octylamine, and hexamethylenimine in 1.0 mol/L aqueous sodium hydroxide with a 5% excess of benzenesulfonyl chloride gave, respectively, 94%, 98%, and 97% yields of the corresponding sulfonamides. Key words: sulfonyl chlorides, primary and secondary amines, pHyield profiles, organic synthesis in water, hydrophobic effects.
Acid enol and dihydropyridine intermediates in pyridylketene hydration  A computational study
Authors: Fedorov Andrei V , Najafian Katayoun , Tidwell Thomas T , Vukovic Sinisa
Published: January 2006

3-Pyridylketene (3-1) is found experimentally to undergo hydration forming an intermediate acid enol 3-2; whereas 2- and 4-pyridylketenes (2-1 and 4-1), instead, form (carboxymethylene)dihydropyridine intermediates 2-4 and 4-4, which live much longer than 3-2. Density functional calculations have been carried out to elucidate the hydration reactivity of these ketenes, and reveal that the dihydropyridine intermediates 2-4 and 4-4 are more stable than the unobserved acid enols 2-2 and 4-2 by 6.23 and 12.2 kcal/mol, respectively. For 3-1 a pathway was calculated utilizing two H2O molecules leading to the acid enol intermediate 3-2, which then forms 3-pyridylacetic acid (3-3). Hydration of 4-pyridylketene involves net 1,6-addition of water, and a pathway involving a bridge of six H2O molecules connecting the pyridyl nitrogen and the carbonyl carbon was determined. Key words: mechanisms of pyridylketene hydration, computations, enols, dihydropyridines.
Physical organic chemistry in Canada 19002005
Authors: Tidwell Thomas T
Published: January 2006

Some of the history of the development of physical organic chemistry in Canada from the 1920s is presented, including many of the individuals involved, and their major areas of interest.Key words: history of physical organic chemistry in Canada, organic reaction mechanisms, free radicals, kinetics.
The detrimental effect of orotic acid substitution in the peptide nucleic acid strand on the stability of PNA2:NA triple helices
Authors: Hudson Robert HE , Wojciechowski Filip
Published: January 2006

We have investigated the incorporation of C6 derivatives of uracil into polypyrimidine peptide nucleic acid oligomers. Starting with uracil-6-carboxylic acid (orotic acid), a peptide nucleic acid monomer compatible with Fmoc-based synthesis was prepared. This monomer then served as a convertible nucleobase whereupon treatment of the resin-bound methyl orotate containing hexamers with hydroxide or amines cleanly converted the ester to an orotic acid or orotamide-containing peptide nucleic acid. Peptide nucleic acid hexamers containing the C6-modified nucleobase hybridized to both poly(riboadenylic acid) and poly(deoxyriboadenylic acid) via triplex formation. Complexes formed with poly(riboadenylic acid) were more stable than those formed with poly(dexoyriboadenylic acid), as measured by temperature-dependent UV spectroscopy. However, both of these complexes were destabilized relative to the complexes formed by an unmodified peptide nucleic acid oligomers. Internal or doubly substituted hexamers are destabilized more strongly than a terminally substituted one, and the type of substitution (carboxamide, ester, carboxylic acid) affects the overall triplex stability. These results clearly show that incorporation of a C6-substituted uracil into polypyrimidine PNA is detrimental to triplex formation. We have also extended this chemistry to incorporate uracil-5-methylcarboxylate into a peptide nucleic acid hexamer. After on-resin conversion of the C5 ester to the 3-(N,N-dimethylamino)propylamide, significant stabilization of the triplex formed with poly(riboadenylic acid) was observed, which illustrates the compatibility of C5 substitution with peptide nucleic acid directed triple helix formation. Key words: peptide nucleic acid, triple helix, orotic acid, orotamide, PNA.
Synthesis and structural characterization of zinc complexes of the imidoamido phosphate anions OP[(NHR)3x(NR)]x (R = Me, t-Bu; x = 13) and EP[(NH-t-Bu)2(N-t-Bu)] (E = S, NSiMe3)
Authors: Armstrong Andrea F , Chivers Tristram , Krahn Mark , Parvez Masood
Published: January 2006

The reaction of OP(NH-t-Bu)3 with 1 equiv. of ZnMe2 generates the dimeric eight-membered ring {MeZn[(µ-NH-t-Bu)(µ-N-t-Bu)P(NH-t-Bu)(µ-O)]}2 (5) and the cubane {[MeZn]3[OP(N-t-Bu)3][OP(NH-t-Bu)3]} (6), which contains the first known trisimidophosphate trianion. A related complex {Zn[ZnMe]2[OP(N-t-Bu)(NH-t-Bu)2][OP(N-t-Bu)3]} (7) is obtained by the reaction of OP(NH-t-Bu)3 with ZnMe2 in a 2:3 molar ratio. The treatment of OP(NHMe)3 with 1 equiv. of ZnMe2 produces the oxide-templated cluster {Zn4(µ4-O)[OP(NMe)(NHMe)2]4[OP(NMe)2(NHMe)]}2 (8). Each half of this centrosymmetric dimer contains a tetrahedral arrangement of four 4-coordinate Zn2+ ions surrounding the central µ4-O2- anion. The reaction of SP(NH-t-Bu)3 with ZnMe2 in a 1:1 molar ratio generates the dimer {MeZn(µ-S)(µ-N-t-Bu)P(NH-t-Bu)2}2 (10), which has a ladder-type structure. When a 2:1 molar ratio of the same reagents is employed, the bis(N,S)-chelated complex {Zn[(µ-S)(µ-N-t-Bu)P(NH-t-Bu)2]2} (11) is obtained. The monomeric N,N′-chelated complex {MeZn[(µ-N-t-Bu)(µ-NSiMe3)P(NH-t-Bu)2]} (12) results from the reaction of Me3SiNP(NH-t-Bu)3 with 1 equiv. of dimethylzinc. All new compounds have been characterized by multinuclear (1H, 13C, and 31P) NMR spectroscopy and, in the case of 5, 6, 7, 8, and 10, by X-ray structural determinations.Key words: zinc, phosphate, imido ligands, sulfur.
Microwave- and ultrasound-assisted semisynthesis of natural methoxylated propiophenones from isomeric mixture of phenylpropenes in minutes
Authors: Joshi Bhupendra P , Sharma Anuj , Sinha Arun K
Published: January 2006

A rapid and practical semisynthesis of natural methoxylated propiophenones (3a3f) is realized by reacting stereo- and regio-isomeric mixture of phenylpropenes (1a1f) with a catalytic amount of palladium chloride  sodium formate in formic acid, methanol, and water (2:1:2) into single product phenylpropanes (2a2f) followed by its oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in wet dioxane, containing a few drops of formic acid. Conventional, ultrasound, and microwave heating were compared through these studies.Key words: focused microwave, ultrasound, phenylpropene, propiophenone, DDQ.
Enhancing image quality of scanning electrochemical microscopy by improved probe fabrication and displacement
Authors: Zhu Renkang , Ding Zhifeng
Published: January 2006

Scanning electrochemical microscopy (SECM) is a powerful tool for its wide applications in determining charge transfer kinetics, imaging chemical reactions and topography, as well as fabricating microstructures at various interfaces and (or) surfaces. Imaging applications, in particular, rely on the natures of SECM probes and the scanning systems to move them in the vicinity of interfaces. While progress has been made in new approaches to tip fabrication, there are few reports on the improvement of the tip positioning system to enhance SECM image quality. We have recently built an advanced SECM setup using a closed-loop scanning system and improved probe fabrication and characterization procedures. Here we will describe this development, as well as the application of these techniques to greatly improve the quality of SECM images. Video micrograph, cyclic voltammograms, and SECM approach curves (current vs. tipsubstrate distance) were chosen to characterize probe quality and to determine the ratio of electrode diameter to glass sheath diameter. The SECM setup has a resolution and repeatability of 20 nm in three dimensions (x, y, and z) and can locate and relocate areas of interest precisely after a coarse image. Interdigitated electrode arrays of platinum and gold were first imaged. Image resolution revealed by sharpness of Pt band edges was enhanced by using a 2 µm diameter electrode. Pt or Au band height was found to be around 80200 nm by fitting the approach curves to the theoretical ones. Imaging conditions such as delay time for a large step size between two succeeding data points were optimized. To test its thermal and temporal stability, the system was then used to image letters, which were printed on a transparency with font bold Courier New and font size 2. Minor drifts were found during the image process up to the experimental length of 8 h and 45 min. Letter thickness was found to be 1.01.2 µm. A silicon substrate with an array of square pits spaced apart on 10 µm centers was finally imaged. Good quality images were obtained at various tipsubstrate distances even though the squares were just as small, if not smaller, than the tip. The samples were also imaged by AFM for comparison.Key words: scanning electrochemical microscopy, atomic force microscopy, microelectrode fabrication, closed-loop imaging, probe approach curve.
A new method for evaluation of the mobility of silica-grafted alkyl chains by suspension-state 1H NMR
Authors: Derakhshan Mahnaz , Ansarian Hamid R , Rahman M Mizanur , Sakurai Toshihiko , Takafuji Makoto , Ihara Hirotaka
Published: January 2006

Although molecular mobility is usually probed by measurement of the T1 relaxation time, it is not the case for methylene groups of grafted acyl chains because each methylene group has a different mobility and hence, a different T1 relaxation time depending on the distance from the junction between organic molecule and nonorganic particle. Therefore, we devised a very simple method that can semiquantitatively determine the extent of mobility in the grafted acyl chains. Silica-supported poly(octadecylacrylate) (Sil-ODAn), polymeric octadecylsilyl silica (polymeric ODS), and monomeric octadecylsilyl silica (monomeric ODS) were studied by comparing the intensity of NMR peaks from grafted molecules with the same amount of nongrafted molecules. In the case of Sil-ODAn, with a gradual increase in temperature, the intensity of the proton signals (1H NMR) of the octadecyl moieties (mainly methylene groups) rose dramatically. This dramatic rise was at the same temperature as that of an endothermic peak detectable in its DSC thermogram, indicating a relatively complete solid to liquid phase transition. Sil-ODAn, as the stationary phase in RP-HPLC, showed analogous temperature dependencies of the separation factor between naphthacene and triphenylene (as a simple indicator of shape selectivity). Using this method we determined the liquid phase percentage (LPP) in Sil-ODAn, polymeric ODS, and monomeric ODS at various temperatures. We suggest LPP as a semiquantitative index of mobility for grafted organic layers.Key words: comb-shaped polymer, nanocomposite, alkyl chain mobility, NMR, liquid chromatography.
Provenance-dependent variability of Abies grandis stem form under mountain conditions of Beskid Sądecki (southern Poland)
Authors: Socha Jarosław , Kulej Marian
Published: January 2006

This study compared the stem form of different provenances of Abies grandis Lindl. under the mountain conditions of Poland. Seven partial populations of this species, originating from two regions in its natural range, were tested. It was concluded that creating separate stem form models is an effective method for comparing stem forms, because the model curves for the groups under comparison are not affected by tree dimensions. The results of this study showed distinct variation in the tested populations of A. grandis in respect to stem form according to provenance (genotype). These differences are particularly evident between provenances from the different regions determined by Müller (K.M. Müller. 1935. Mitt. Deutcsh. Dendrol. Ges. 44: 54123 and K.M. Müller. 1936. Mitt. Deutcsh. Dendrol. Ges. 47: 82132). In general terms, trees representing provenances from region II are characterized by greater cylindricity in comparison with trees from region I. At equal DBH and height, the volume of trees from regions I was smaller than the volume of trees from region II by an average of approximately 7.6%.
Anthropogenic impact on past and present fire regimes in a boreal forest landscape of southeastern Norway
Authors: Groven Rune , Niklasson Mats
Published: January 2006

Fire-scarred wood samples from 50 stumps, snags, and living trees of Scots pine (Pinus sylvestris L.) were dendrochronologically cross-dated to describe an 800 year long fire history of Eldferdalen Nature Reserve (~6 ha) and its surroundings (~4000 ha) in southeastern Norway. In the western part of the study area, we recorded 55 different fires within a 200 ha area around the reserve between 1511 and 1759 and a mean fire interval in single samples of 24.6 years. The composite mean fire interval for the nature reserve was 10.5 years. Fire intervals were longer in the eastern part of the study area, with a single sample mean fire interval of 49.1 years. Only three fires were detected after 1759, the last one in 1822. Based on historical accounts, we assume that the high number of fires and short fire intervals were influenced by deliberate ignition for agricultural purposes, most likely burning to improve the conditions for cattle grazing and slash-and-burn cultivation. We suggest that the cessation of fires was influenced by the increased value of timber and mining activity, thereby leading to increased interest in conservation of the timber resources.
Windthrow hazard modelling in boreal forests of black spruce and jack pine
Authors: Elie Jean-Gabriel , Ruel Jean-Claude
Published: January 2006

In this study we compare the mechanical resistance of black spruce (Picea mariana (Mill.) BSP) and jack pine (Pinus banksiana Lamb.) and quantify the effect of species, forest cover type, and soil conditions on tree stability. To measure tree resistance to an applied load, 85 trees were pulled over using a cable and winch system. Predictive equations for the maximum turning moment that a tree can withstand (Mc) were developed with stem mass, and the other factors were used as explanatory variables. The presence of jack pine within the stand negatively affected black spruce resistance. In mixed stands, Mc was significantly influenced by the interaction between tree species and soil type. Jack pine was the only species with significantly lower resistance when grown on shallow and stony soils, which are likely to restrict root development. Black spruce resistance was not affected by soil conditions. Preliminary calculations of critical wind speeds required to cause damage using an adaptation of the ForestGALES model were much lower than those previously published for black spruce.
Tamarack response to salinity: effects of sodium chloride on growth and ion, pigment, and soluble carbohydrate levels
Authors: Renault Sylvie
Published: January 2006

The extraction of bitumen from oil sands can increase levels of sodium and chloride in boreal forest soils. A study was designed to test the effect of 30 and 60 mmol/L NaCl on 6-month-old tamarack (Larix laricina (Du Roi) K. Koch.) seedlings grown in aerated nutrient solutions. After 40 days of treatment in a growth chamber, 30 mmol/L NaCl caused injury to old needles and decreased shoot biomass, root potassium concentration, root soluble carbohydrate content, as well as chlorophyll a, chlorophyll b, and carotenoid levels in old needles. Sodium content of seedlings exposed to 30 mmol/L NaCl was higher in roots than in stems and new needles, while chloride content was higher in both old and new needles. Sodium and chloride concentrations were similar in new needles and in old needles. Seedlings exposed to 60 mmol/L NaCl showed injury in both old and new needles and lower root and shoot biomass, root magnesium and potassium concentrations, and both root and stem soluble carbohydrate levels. Furthermore chlorophyll a, chlorophyll b, and carotenoid levels were lower in all needles than in the control. Sodium and chloride contents of seedlings treated with 60 mmol/L NaCl were higher in old and new needles than in roots and stems. The results suggest that tamarack seedlings have a moderate tolerance to salinity, and when exposed to 30 mmol/L NaCl the seedlings could avoid injury by maintaining a relatively high K+/Na+ ratio in new needles and controlling Na+ transport to the shoots.
A geostatistical approach to cork production sampling estimation in Quercus suber forests
Authors: Montes Fernando , Hernández María José , Cañellas Isabel
Published: January 2006

The estimation of cork production in cork oak (Quercus suber L.) forests is complex because of the high heterogeneity of stripped surface distribution (the variable used to quantify cork production) and the importance of cork thickness estimation as a determining factor of cork quality. In this study, the different sources of variation in stripped surface ([Formula: see text]d) estimation and the effects of the spatial structure of the variance were analysed. When indicator kriging was used to determine the cork productive area, ordinary kriging and kriging with measurement errors gave better estimations of [Formula: see text]d (ordinary block kriging estimation of 156.16 m2/ha and standard errors (SE) of 16.40 and 15.7 m2/ha, respectively) than the design-based approach for the whole forest area (66.37 m2/ha, SE = 11.34 m2/ha). The SE lying in the second-stage design was 4.93 m2/ha. The ordinary kriging prediction of cork thickness using an XY(λZ) variogram, where λ is the anisotropy coefficient of the Z axis, gives a smaller SE and less bias than the kriging prediction with the XY variogram (for a mean estimation of 21.91 mm, SE = 3.90 and 4.16 mm, respectively, and sum of errors of 0.42 and 0.85 respectively).
The effects of nutrition and density on growth, foliage biomass, and growth efficiency of high-density fire-origin lodgepole pine in central British Columbia
Authors: Blevins David P , Prescott Cindy E , Allen H Lee , Newsome Teresa A
Published: January 2006

A factorial thinning and fertilization experiment was established in central British Columbia in a 36-year-old high-density fire-origin lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) stand to examine the effects of density, nutrition, and their interaction on tree and stand growth, foliage biomass per hectare, and growth efficiency. Volume growth was increased from 2 to 7 m3·ha1·year1 when fertilizer was applied without thinning and to 5 m3·ha1·year1 when fertilizer was applied with thinning. Thinning increased tree-level foliage biomass and growth efficiency by concentrating limited resources onto fewer trees, resulting in increased tree-level volume growth. Stand-level volume growth was reduced by thinning because of the large reduction in stocking. However, by year 4, stand-level volume growth was the same on control and thinned plots, suggesting that thinned trees have already recaptured the site potential. Fertilization increased both tree-level and stand-level productivity through increases in resource availability per tree and per hectare. This resulted in increased foliage biomass and growth efficiency at the tree and stand level. The combination of thinning and fertilization resulted in the greatest tree-level growth because of increased tree-level foliage biomass and growth efficiency. Boron appears to be the most limiting element followed by sulfur and nitrogen.
Fuel treatments alter the effects of wildfire in a mixed-evergreen forest, Oregon, USA
Authors: Raymond Crystal L , Peterson David L
Published: January 2006

We had the rare opportunity to quantify the relationship between fuels and fire severity using prefire surface and canopy fuel data and fire severity data after a wildfire. The study area is a mixed-evergreen forest of southwestern Oregon with a mixed-severity fire regime. Modeled fire behavior showed that thinning reduced canopy fuels, thereby decreasing the potential for crown fire spread. The potential for crown fire initiation remained fairly constant despite reductions in ladder fuels, because thinning increased surface fuels, which contributed to greater surface fire intensity. Thinning followed by underburning reduced canopy, ladder, and surface fuels, thereby decreasing surface fire intensity and crown fire potential. However, crown fire is not a prerequisite for high fire severity; damage to and mortality of overstory trees in the wildfire were extensive despite the absence of crown fire. Mortality was most severe in thinned treatments (80%100%), moderate in untreated stands (53%54%), and least severe in the thinned and underburned treatment (5%). Thinned treatments had higher fine-fuel loading and more extensive crown scorch, suggesting that greater consumption of fine fuels contributed to higher tree mortality. Fuel treatments intended to minimize tree mortality will be most effective if both ladder and surface fuels are treated.
A visual index for estimating cone production for individual white spruce trees
Authors: LaMontagne Jalene M , Peters Susan , Boutin Stan
Published: January 2006

The number of cones produced by coniferous trees is commonly estimated by visual counts from the ground of a portion of the tree multiplied by a simple conversion factor. Linear conversion factors have been used to estimate total cone production by white spruce (Picea glauca (Moench) Voss). However, these conversion factors originate from other coniferous species and were often based on assumptions of cone visibility within the crown and not on empirical data. We propose a simple method for estimating the total number of cones produced by individual white spruce. We counted visible cones (an index of cone production, or cone index) on a total of 60 trees located in Alberta and Yukon, Canada, that were then felled and all cones were counted. We found that log(actual total cones) = 0.073 + 1.189 × log(cone index) is more accurate for estimating total cone numbers for white spruce than are other conversion factors (ranging from total cones = 1.5 × cone index to total cones = 3.35 × cone index), as determined using Akaike's information criterion with small sample bias adjustment and a validation data set. The relationship between the index of cone production and actual total cones produced is nonlinear, which is contrary to that proposed for various Pinus species.