bluuebunny/crossref_metadata_2025 huggingface dataset:
Within-basin fish assemblage structure: the relative influence of habitat versus stream spatial position on local species richness
Authors: Grenouillet G , Pont D , Hérissé C
Published: March 2004

Local species richness (LSR) in stream fish assemblages is related to both local habitat conditions and stream spatial position. In this study, we examined the within-basin distribution of LSR in the Upper Saône River (France). We describe the longitudinal patterns in LSR and assess the relative effects of both local habitat and spatial (upstream and downstream) influences on species richness. We showed that among the different local habitat variables, only stream width and gradient significantly influenced LSR. Spatial factors also influenced the within-basin distribution of LSR and resulted in spatial autocorrelation, highlighting contagious biotic processes in structuring stream fish assemblages. However, we did not confirm other published predictions that headwater streams entering large rivers directly should have greater species richness. The spatial autocorrelation was only significant downstream (from 4th- to 7th-order streams), suggesting that the relative importance of local habitat and biotic processes may depend on the position along the longitudinal gradient.
Biodegradation of 3,3′-dichlorobenzidine in freshwater lake sediments
Authors: Nyman Marianne C , Harden Joel , Nies Loring F , Blatchley III Ernest R
Published: March 2004

3,3′-Dichlorobenzidine (DCB) and its degradation products, 3-chlorobenzidine (MCB) and benzidine, are of environmental concern due to their toxic and carcinogenic nature. Laboratory experiments have been conducted to elucidate the biodegradation behavior of DCB in Lake Macatawa (Holland, Michigan) sediment–water systems at 4, 24, and 30 °C incubation temperatures. Sediment samples varied in pH (6.45–7.41), total organic carbon (OC) content (1.4–17.1), and particle size distribution (silty-clay to sandy). Biodegradation of DCB was observed in non-autoclaved samples that were incubated at 4, 24, and 30 °C for approximately 12 months. The dechlorination rate as a function of OC content was essentially found constant at 4 °C and 24 °C, but demonstrated a roughly linear increase at 30 °C, thereby suggesting that OC content might be correlated to dechlorination rate at 30 °C incubation temperature. The rate as a function of particle size (e.g., <74 µm) did not demonstrate a clearly defined relationship. Key words: 3,3′-dichlorobenzidine, 3-chlorobenzidine, benzidine, biodegradation.
Evaluation of the ability of chlorine to inactivate selected organisms from the biofilm of a drinking water distribution system simulator following a long-term wastewater cross-connection
Authors: Gibbs Shawn G , Meckes Mark C , Green Christopher F , Scarpino Pasquale V
Published: March 2004

The drinking water distribution system simulator (DSS) from the U.S. EPA was operated with a direct cross-connection of 0.3% wastewater to system volume per day for 70 d. During the cross-connection, tap water, wastewater, and system discharge water were monitored to ensure that the wastewater cross-connection was the source of study organisms and that these organisms were present in the water column of the DSS. The effectiveness of free chlorine levels of 0, 1, 2, and 5 mg/L to inactivate microbes in biofilms on PVC and ductile iron coupons following a wastewater cross-connection was determined. A reduction in organisms occurred after 12 h for both non-chlorinated PVC and ductile iron coupons. This suggests that the study organisms were able to adhere to the biofilm, but were not able to remain in the biofilm. The study organisms were inactivated both in the biofilm and in the water column. Water column data showed that biofilm released culturable heterotrophs and endospores into the water column throughout the 72 h evaluation period at all chlorine levels evaluated. Key words: biofilm, chlorine, wastewater, drinking water, microorganisms, cross-connection.
Evaluating the dissolution and natural attenuation of jet fuel at a former tank farm
Authors: Thompson Anne-Marie , Van Geel Paul J , Parker Wayne J
Published: March 2004

Fuel handling practices at the former National Defence tank farm in Ottawa, Canada, resulted in the release of jet fuel to the subsurface. A site investigation was undertaken to determine the extent of the contamination and to evaluate the effectiveness of natural attenuation as a remedial alternative for the contaminated groundwater. A soil-vapour study and borehole and test pit soil samples aided in conceptualizing the residual jet fuel source term. BioRedox-MT3DMS was used to simulate the dissolution of the multicomponent jet fuel and the subsequent transport and biodegradation of the various hydrocarbon components in the underlying aquifer. The model was able to simulate and support the data collected at the site to indicate that natural attenuation processes were effectively reducing contaminant concentrations and mass, and that the spatial extent of the plume had effectively reached a steady state. In addition, the model indicated that the source term would remain for many years due to the slow dissolution and biodegradation rates of the heavier hydrocarbons. Key words: natural attenuation, NAPL dissolution, biodegradation, modelling, BioRedox-MT3DMS, jet fuel, petroleum hydrocarbons, redox conditions.
Sediment entrainment during pipeline water crossing construction: predictive models and crossing method comparison
Authors: Reid S M , Ade F , Metikosh S
Published: March 2004

Sediment entrained during pipeline water crossing construction has the potential to adversely affect downstream aquatic biota and their habitats. Past construction monitoring studies were used to derive equations for the prediction of peak and mean sediment entrainment rates associated with different phases of open-cut (wet) construction. Correlation coefficients and suspended sediment concentrations measured downstream of simulated open-cut crossings indicate that entrainment equations more closely predict mean concentrations as compared to peak concentrations. The same data set was used to demonstrate that isolated (dam and pump or flumed) crossing methods were effective at reducing the amount of sediment released during pipeline installation underneath small to medium sized watercourses. The effectiveness of isolated crossing methods was in some cases limited by pump failure or insufficient capacity, dam failure, poor dam seals, and poor containment of pumped ditch water. Key words: pipeline construction, sediment, best management practices, impact assessment.
Ammonia removal from an aqueous solution by the use of a natural zeolite
Authors: Njoroge B N.K , Mwamachi Slade Gilbert
Published: March 2004

A series of batch experiments were conducted to ascertain the ability of a natural zeolite (a crystalline aluminosilicate) to remove ammonia from synthetic wastewater samples composed of ammonium hydroxide (NH4OH). The reaction with ammonia was observed to be very rapid, with half the amount of ammonium ions being sorbed in the first minute in some instances. Estimated ammonia uptake was favoured by low sorbate concentration, small particle size of sorbent, high temperature, and an alkaline medium. The sorption kinetics studies strongly indicated that the sorption process was largely governed by intraparticle pore diffusion. The effect of temperature on equilibrium at 14 °C and at room temperature (25 °C) showed the sorption process was endothermic, the rate and extent of sorption increasing appreciably with temperature. The equilibrium data fitted the Langmuir sorption model, a possible indication of a monolayer coverage of ammonium ions on the surface of the particle. The Langmuir correlation of the equilibrium data suggested that ion exchange might have been the dominant sorption mechanism. The zeolite seemed to have some fairly good potential for ammonia removal with the sorption capacity being about 4 mmol (NH4+) per 100 g of sorbent. However, this needs to be investigated further through flow-through conditions and in the presence of other ions as in real wastewater. Key words: zeolite, aluminosilicate, sorbent, ammonia nitrogen, sorption, sorbate.
Degradation of monoethanolamine in soil
Authors: Ndegwa Anne W , Wong Ron C.K , Chu Angus , Bentley Laurence R , Lunn Stuart R.D
Published: March 2004

Monoethanolamines (MEA) are commonly used by the natural gas industry to remove acid gases from the natural gas stream. A series of pan studies was conducted to examine the biodegradability of MEA in soil recovered from a gas plant site under various environmental conditions. Experimental results indicate that MEA was successfully biodegraded or transformed into other compounds under both aerobic and anaerobic conditions even at concentrations greater than 1500 mg/kg. Ammonium, acetate, and nitrogen gas were the dominant by-products in these experiments. The generation of nitrogen gas suggests that simultaneous nitrification and denitrification occurred because of the existence of anoxic zones resulting from diffusion limited oxygen transport into the soils. Cold temperatures (5 °C) reduced the biodegradation rates significantly compared to rates at room temperature. Key words: bioremediation, monoethanolamine, ammonia, acetate, pan study, cold temperature.
Vacuum pyrolysis of N,N-dimethyl bicyclo[3.2.0]hepta-3,6-dien-1-amine  He I ultraviolet photoelectron spectroscopic and computational studies
Authors: Bajorek Tom , Werstiuk Nick H
Published: March 2004

The photoelectron spectra of N,N-dimethylbicyclo[3.2.0]hepta-3,6-dien-1-amine (1) and its pyrolysate were obtained using an unique ultraviolet (UV) photoelectron (PE) spectrometer interfaced with a CW CO2 laser. Pyrolysis of 1 in the source chamber of the PE spectrometer initially generates the transient N,N-dimethylcyclohepta-1E,3Z,5Z-trien-1-amine (2)  the computed barrier is 21.5 kcal mol1  that isomerizes to the all-cis isomer with a barrier of only 5.0 kcal mol1. There is no evidence for the formation of N,N-dimethycyclohepta-1Z,3E,5Z-trien-1-amine (4), formation of which has an zero-point-energy corrected barrier of 28.4 kcal mol-1. A PE spectrum of an authentic sample of N,N-dimethylcyclohepta-1Z,3Z,5Z-trien-1-amine (3) correlated well with the pyrolysis spectrum. Molecular orbitals and their energies were obtained with Becke3LYP calculations.Key words: vacuum pyrolysis, N,N-dimethylbicyclo[3.2.0]hepta-3,6-dien-1-amine, photoelectron spectroscopy, DFT calculations.
Bismuth-mediated reductive dehalogenation of α-halocarbonyl compounds
Authors: Lee Yoon Joo , Chan Tak Hang
Published: March 2004

Bismuth metal, activated by ammonium hydrogen fluoride, was found to reduce various α-halocarbonyl compounds efficiently and chemoselectively in aqueous media to give the dehalogenated reduction products in excellent yields.Key words: bismuth, reduction, α-halocarbonyl compounds, fluoride salts, aqueous media, bismuth enolates, aldol reaction.
Generic synthesis of β-sultams via domino alkylation of bromomethanesulfonamides
Authors: Barton William R , Paquette Leo A
Published: March 2004

Reaction of N-substituted bromomethanesulfonamides with 2 equiv of potassium carbonate and an α-halo ketone, ester, or nitrile leads directly to 3-substituted β-sultams. The first step is intermolecular and is followed by an intramolecular alkylation. The process is particularly efficient when diethyl bromomalonate and 3-chloro-2-butanone are involved. In the latter example, no competitive cyclization to form a six-membered ring is seen. The functional groups in certain of the β-sultam products can be subsequently manipulated to give bicyclic products.Key words: β-sultams, intramolecular SN2 displacement, sulfonamides, ring closing metathesis, four-membered heterocycles.
Regiospecific synthesis of alkylphenanthrenes using a combined directed ortho and remote metalation  SuzukiMiyaura cross coupling strategy
Authors: Cai Xiongwei , Brown Stephen , Hodson Peter , Snieckus Victor
Published: March 2004

Using a combined directed ortho metalation (DoM)  SuzukiMiyaura cross coupling  directed remote metalation (DreM) approach, the alkylphenanthrenes (APs) 1-methyl- (5a), 1,7-dimethyl- (5b), 2,7-dimethyl- (5c), 7-ethyl-1-methyl- (15), and 7-tert-butyl-1-methylphenanthrenes (27) have been synthesized in four to seven steps and 21%36% overall yields. In contrast to classical protocols, this method, which may be scaled to gram quantities, provides single isomers of APs in high purity of value as analytical standards for environmental studies. Aminocarbonylation of triflates to N,N-diethylbenzamides (9 [Formula: see text] 10) and anionic Fries rearrangement (23 [Formula: see text] 24) provide other potential links to DoM chemistry.Key words: phenanthrene, directed ortho metalation, SuzukiMiyaura cross coupling, synthesis, polycyclic aromatic hydrocarbon, carbonylation.
Synthetic studies on cyathin diterpenes - Total synthesis of (±)-allocyathin B3
Authors: Ward Dale E , Gai Yuanzhu , Qiao Qi , Shen Jianheng
Published: March 2004

The synthesis of racemic allocyathin B3 from an advanced intermediate possessing the ring system and relative stereochemistry but lacking the isopropyl and hydroxymethyl groups is reported. The isopropyl group was introduced by radical cyclization of a methyl propargyl acetal of an α-bromoketone and the hydroxymethyl group was generated by Pd-catalyzed carbonylation of a vinyl triflate. The route provides functionalized intermediates that could allow access to more complex members of the cyathin family of diterpenes. Several modifications and improvements to the procedures previously described for the synthesis of the advanced intermediate have been achieved.Key words: cyathin diterpenes, cyathanes, allocyathin B3.
New 1,3-dihydroazepin-2-one derivatives by [3,3]-sigmatropic rearrangement of suitably substituted 2-alkenylcyclopropyl isocyanates
Authors: Reissig Hans-Ulrich , Böttcher Gesine , Zimmer Reinhold
Published: March 2004

The 2-siloxysubstituted 2-alkenylcyclopropanecarboxylic acids 1014 were converted into the corresponding carbonyl azides by treatment with DPPA (diphenyl phosphorazidate) and triethylamine. On heating to 80 °C these intermediates smoothly furnished azepinone derivatives 1925 in moderate to good overall yields, which are the result of a sequence of Curtius reaction to cyclopropylisocyanates, [3,3]-sigmatropic rearrangement, and a final proton shift. The primary products may undergo desilylation (to afford azepin-2,5-diones such as 23) or double bond migration (to compound 25). Cyclopropanecarboxylic acids cis-32, cis-34, and cis-35, which bear no 2-siloxy group, similarly provided azepinone derivatives 3638 in good yields. No influence of the 2-siloxy substituent on the reaction course and rates could be observed in these qualitative studies, which was confirmed by DFT calculations with model compounds 3942 showing similar reaction barriers for rearrangements of cyclopropylisocyanates with or without a 2-hydroxy group.Key words: vinyl cyclopropanes, carbonylazides, [3.3]-sigmatropic rearrangements, azepinones.
Role of trinuclear Zn(II) complexes in promoting the hydrolysis of 4-nitrophenyl acetate
Authors: Ge Qing-Chun , Guo Yan-He , Lin Hai , Gao Dong-Zhao , Lin Hua-Kuan , Zhu Shou-Rong
Published: March 2004

Potentiometric determination shows that trinuclear Zn(II) complexes of the four tripods 1,3,5-tri(2′,5′-diazahexyl)benzene (L1), 1,3,5-tri(2′,5′-diazaheptyl)benzene (L2), 1,3,5-tri(2′,5′-diazaoctyl)benzene (L3), and 1,3,5-tri(2′,5′-diazanonyl)benzene (L4) could be potential hydrolytic catalysts. CH3CN solutions containing [3Zn:L]T (0.5~2 × 103 mol·dm3) with I = 0.10 mol·dm3 of KNO3 and Good's buffer (10% volume fraction) were studied for the catalyzing hydrolysis of p-nitrophenyl acetate (NA, 0.5~2 × 103 mol·dm3), at 298 K, in the 6.58.2 pH range. The observed rate constants, kobs, fit the equilibrium equation kobs = kcom [3Zn:L]T + kOH[OH] + k0. The sigmoid pH~kcom profiles for NA hydrolysis suggest that either the Zn(II)-bound hydroxyl or the Zn(II)-bound water forms of the catalysts can be the active species. The observed second-order rate constants are 0.0082, 0.011, 0.0059, and 0.0019 mol1·dm3·s1 for the four Zn3LH2O complexes (kA) and 0.342, 0.257, 0.382, and 0.091 mol1·dm3·s1 for the four Zn3LOH- groups (kB), respectively. However, under the condition that [NA] = 0.5 × 103 mol·dm3 and [3Zn:L1]T = 2~4 × 102 mol·dm3 at pH 7.6, the observed rate constants, kobs, obey the equilibrium kobs = kcom[3Zn:L]T/(1/K′ + [3Zn:L]T). This indicates that the 3:1 complex (or its deprotonated hydroxide form) mediates NA hydrolysis by nucleophilic attack of the carboxyl center with the pre-formation of a coordination bond between the carboxyl oxygen atom and the Zn(II) ion. Comparison with other models was made, and the reasons for the high catalytic efficiency of the tripodal complexes were given.Key words: tripod, Zn(II), catalysis, NA hydrolysis, polynuclear.
Neat reaction microwave technology for the synthesis of N-substituted-1,4-dihydropyridines
Authors: Kidwai Mazaahir , Mohan Richa
Published: March 2004

Hantzsch synthesis of N-substituted-1,4-dihydropyridines (1,4-DHP) was carried out using an environmentally benign procedure. Neat reactants were subjected to microwave irradiation (MWI) to give the required products in excellent yield. Appreciable results were not obtained when conventional synthesis using neat reactants was carried out. The good yield and rate enhancement observed in the case of microwave irradiation is attributed to the uniform heating effect of microwaves.Key words: 1,4-dihydropyridines (1,4-DHP), microwave irradiation (MWI), neat reaction, solid support.
Reactions of phenyldimethylsilyllithium with β-N,N-dimethylaminoenones: A convenient synthesis of β-dimethyl(phenyl)silylacrylic acid and its derivatives
Authors: Fleming Ian , Marangon Elena , Roni Chiara , Russell Matthew G , Chamudis Sandra Taliansky
Published: March 2004

Phenyldimethylsilyllithium reacted with 5,5-dimethyl-3-(N,N-dimethylamino)cyclohex-2-enone (7), 3-(E)-N,N-dimethylaminopropenal (11), and 4-N,N-dimethylaminobut-3-en-2-one (13) to give the corresponding β-silyl-α,β-unsaturated carbonyl compounds 8, 12, and 14, in which the dimethylamino group has been displaced by the phenyldimethylsilyl group. Phenyldimethylsilyllithium reacted with ethyl β-N,N-dimethylaminopropenoate (15) by conjugate addition, but, in contrast to the ketones 7 and 13 and the aldehyde 11, the intermediate enolate 16 was C-protonated in the aqueous work-up to give ethyl 3-N,N-dimethylamino-3-dimethyl(phenyl)silylpropanoate (17). When the enolate 16 was instead given a mysteriously brief treatment with methyl iodide before work-up, the product was ethyl 3-(E)-dimethy(phenyl)silylpropenoate (18). Phenyllithium and methyllithium also added conjugatively to ethyl β-N,N-dimethylaminoacrylate (15) but, in contrast to the silyl case, the intermediate enolate 22 reacted unexceptionally with methyl iodide to give the products 25 and 26 of stereoselective C-methylation. This synthesis of the ester 18 was used to synthesize the Oppolzer sultam derivative 30.Key words: conjugate addition, elimination, substitution, silyllithium, silylenone.
Bifunctional bis(oxazolines) as potential ligands in catalytic asymmetric reactions
Authors: Hanessian Stephen , Jnoff Eric , Bernstein Noemy , Simard Michel
Published: March 2004

C2-symmetrical bis(oxazoline) ligands bearing pendant alkylthio ether groups were synthesized, and the structures of Cu complexes were determined by single crystal X-ray diffraction. The potential utility in catalysis was shown in the asymmetric addition of methyllithium to an aromatic aldimine, which resulted in a mixture of products with an enantiomeric excess of 68%.Key words: two-center catalysis, bis(oxazoline), aldimine, imine alkylation.
Radio labelling of the gibberellin plant growth inhibitor 16,17-dihydro-GA5
Authors: Beck Ellen J , Twitchin Bruce , Mander Lewis N
Published: March 2004

An improved five-step procedure has been developed for the synthesis of the gibberellin plant growth inhibitor 16,17-dihydro-GA5 from gibberellic acid. The 3-13C and 3-14C derivatives of this material have also been prepared by excising C-3 from the carbon skeleton (ozonolysis of a Δ2-alkene derivative and subsequent retro-Claisen reaction) and then reassembling the A-ring by means of an intramolecular aldol reaction.Key words: gibberellin, growth inhibitor, degradation, Radio labelling, Wittig reaction.
Efficient construction of benzohydrindenones from aryltrienones via domino Nazarov electrocyclization  electrophilic aromatic substitution
Authors: Browder Cindy C , Marmsäter Fredrik P , West F G
Published: March 2004

1,4-Dien-3-ones substituted with pendant arylethyl side chains attached at C-1 were readily prepared from substituted dihydrocinnamaldehydes. Treatment with TiCl4 at low temperature effected domino Nazarov electrocyclization  arene trapping within 5 min to give racemic benzohydrindenones in near-quantitative yield and with complete diastereoselectivity.Key words: domino process, electrophilic aromatic substitution, Lewis acid, Nazarov cyclization.
RZnI vs. R2Zn in Pd(0)-catalyzed cross-coupling reactions with thioimidates
Authors: Roberts William P , Ghosh Indranath , Jacobi Peter A
Published: March 2004

Thioimidates 1-Z undergo facile cross-coupling with Pd(0)RZnI but are inert to Pd(0)R2Zn. This difference is due to the lower Lewis acidity of R2Zn, as opposed to lower nucleophilicity. Various sources of RZnI (R = Me, Et) and Pd(0) were evaluated for their convenience and reactivity.Key words: thioimidates, cross-coupling, dialkylzincs, alkylzinc iodides.
Mono- and disubstitutions of (hepta-2,5-diyne-1,7-diol) bis(dicobalt) derivatives  Selectivity in Nicholas reactions
Authors: Guo Richard , Gibe Romelo , Green James R
Published: March 2004

Bis(hexacarbonyldicobalt) complexes of benzyl ether  methyl ether or benzyl ether  acetate derivatives of hepta-2,5-diyne-1,7-diols undergo selective Lewis-acid-mediated Nicholas reactions with enol silanes, silyl ketene acetals, and allylstannanes, preferentially replacing the methyl ether or acetate function. Hydride nucleophiles are similarly incorporated selectively using a benzyl ether  alcohol derivative. Subsequent Nicholas reaction at the benzyloxy-bearing site may be accomplished with an identical or a different nucleophile, affording skipped 1,4-diyne-Co4(CO)12 complexes. In instances of lower selectivity for monosubstitution reactions with benzyl ethers, reverting to the use of a menthyl ether  methyl ether complex gives much improved selectivity for methyl ether substitution.Key words: cobalt alkyne complexes, Nicholas reaction, Lewis acids, 1,4-diynes.
Syntheses, crystal structures, and magnetism of one-dimensional complexes generated from copper(II) and carbamyldicyanomethanide bridging ligand
Authors: Shi Jing-Min , Liu Qing-Yun , Xu Wen , Meng Lin , Cheng Peng , Zhao Bin , Yu Wen-Tao
Published: March 2004

Two one-dimensional chain complexes, {[Cu(cda)2H2O]·H2O}n (1) and {[Cu(cda)(H2O)2]·(ClO4)·3H2O}n (2) (cda = carbamyldicyanomethanide anion) have been synthesized and their crystal structures determined by X-ray crystallography. The copper(II) ions in 1 are bridged by two µ1,5-cda bridging ligands, whereas in 2 the copper(II) ions are connected by a single µ1,5-cda ligand. Complex 1 is red while 2 is green. Variable-temperature magnetic susceptibility data indicate that there is a very weak antiferromagnetic interaction between the bridged copper(II) ions in both 1 and 2.Key words: synthesis, crystal structure, copper complex, polynitrile ligand, magnetism.
Testing forest ecosystem management in boreal mixedwoods of northwestern Quebec: initial response of aspen stands to different levels of harvesting
Authors: Brais S , Harvey B D , Bergeron Y , Messier C , Greene D , Belleau A , Paré D
Published: March 2004

The SAFE (sylviculture et aménagement forestiers écosystémique) project was set up in 1998 in the Lake Duparquet Research and Teaching Forest to test stand-level silvicultural treatments designed to reflect different aspects of natural forest dynamics. In the winter of 19981999, four levels of forest harvesting, including a no-harvest and a clearcut treatment, were applied to even-aged trembling aspen (Populus tremuloides Michx.) stands according to a complete block design with three replications. Two partial cut treatments removed 33% and 61% of the stand basal area. During the first growing season, harvesting induced a large increase in indigenous understorey biomass that paralleled changes in the canopy opening. Aspen sucker density increased from 4916 stems/ha in the control to 28 751 and 63 333 stems/ha in the one-third and two-thirds harvesting treatments and 102 916 stems/ha in the clearcut. Most changes in nutrient cycling occurred in the second year and included an increase in forest floor organic C, total N, and base cation availability and a decrease in microbial C/N ratio. These changes may have occurred in response to reduced vegetation uptake and woody debris abundance.
Influence of landscape structure on patterns of forest fires in boreal forest landscapes in Sweden
Authors: Hellberg Erik , Niklasson Mats , Granström Anders
Published: March 2004

To analyze the effect of landscape structure (viz. amount of wetlands) on the past forest fire regime in boreal Sweden, we reconstructed detailed fire histories by cross-dating fire scars in living and dead Scots pine (Pinus sylvestris L.) in two different landscape types: mire-free landscapes with a low proportion (1%2%) of mires and mire-rich landscapes with a high proportion (21%33%) of mires. Two localities were selected and at each one, adjacent mire-free and mire-rich areas of 256601 ha were sampled. Over the studied 650-year period, the two landscape types differed primarily in the fire intervals and sizes of fires. In the mire-rich landscapes, fires had frequently stopped against mire elements. The net effect was significantly longer fire intervals in the mire-rich than in the mire-free landscape (on average, 32 versus 56 years). The mire-rich areas also had a tail of very long fire intervals lacking in the mire-free areas (maximal interval 292 years). We conclude that mires can have a profound effect on both spatial and temporal patterns of forest fires in the boreal forest, but only when they are effective fuel breaks (i.e., they are wet enough) at the time the fires burn and if they truly dissect the nonmire portion of the forest landscape.
Decadal observations of tree regeneration following fire in boreal forests
Authors: Johnstone Jill F , Chapin III F S , Foote J , Kemmett S , Price K , Viereck L
Published: March 2004

This paper presents data on early postfire tree regeneration. The data were obtained from repeated observations of recently burned forest stands along the Yukon  British Columbia border and in interior Alaska. Postfire measurements of tree density were made periodically for 2030 years, providing direct observations of early establishment patterns in boreal forest. Recruitment rates of the dominant tree species in both study areas were highest in the first 5 years after fire, and additional net establishment was not observed after 10 years. The postfire population of spruce (Picea mariana (Mill.) BSP and Picea glauca (Moench) Voss s.l.) remained constant after the first decade in the two study areas. Populations of aspen (Populus tremuloides Michx.) and lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) both declined after 10 years in mixed-species stands along the Yukon  British Columbia border. Mortality rates of aspen and pine were positively correlated with their initial densities, indicating that thinning occurred as a density-dependent process. At all sites, measurements of stand density and composition made early were highly correlated with those made late in the monitoring period, indicating that patterns of stand structure initiated within a few years after fire are maintained through subsequent decades of stand development.
Estimating the impacts of harvest distribution on road-building and snag abundance
Authors: DeLong S Craig , Fall S Andrew , Sutherland Glenn D
Published: March 2004

Various patterns of harvest in forests influence the length of road and number of stream crossings required. Snags are removed directly by harvesting, but they are also removed along road and opening edges to ensure worker safety. To assess the potential impacts of rate of harvest and pattern of harvest in an old-forest-dominated montane landscape, we developed a spatially explicit landscape dynamics model, which includes submodels for snag removal, harvesting activities, and access management. The model assesses the amount of new road construction and number of streams crossed by new roads, as well as changes in snag density and configuration across the landscape over a time horizon of several decades, in response to various harvesting patterns. We estimated that a dispersed 40-ha cutblock harvest pattern required about one-third more kilometres of new road over a 50-year period and removal of up to 70% more snags per hectare of harvest for safety purposes, compared with a harvest pattern based on natural-patch size distribution. Each 20% increase in stand-level retention resulted in a roughly equivalent increase in new road required. Up to eight times as many snags were removed per hectare of harvest for safety purposes at a stand-level retention of 70% than at a stand-level retention of 10%. The model appears to be an effective tool for determining the future impact of various harvest-pattern options on a number of important indicators of ecological impact.
Effects of poisoning nonindigenous slugs in a boreal forest
Authors: Ferguson Steven H
Published: March 2004

This study examined the impact of poisoning nonindigenous slugs on abundance of other soil arthropod groups occurring on the soil surface of a boreal forest. The experimental design consisted of counting soil fauna under boxes from 20 plots during weekly surveys before (year 1) and after (year 2) treatment (metaldehyde poison) with control and experimental plots. Slug abundance was negatively affected by presence of slug poison, with an 80% decrease in slug numbers following treatment. Herbaceous cover did not differ between plots (control and experimental) but the amount eaten decreased (26%15%) with poisoning. Nonindigenous taxa, including slugs, predominated in the macrofauna at this site, accounting for a third of the individuals and a half of the biomass. Possible explanations for the observed patterns in soil arthropod community relative to invasive species are discussed.
The relationship between effective plant area index and Landsat spectral response across elevation, solar insolation, and spatial scales in a northern Idaho forest
Authors: Pocewicz Amy L , Gessler Paul , Robinson Andrew P
Published: March 2004

Leaf area index (LAI) is an important forest characteristic related to photosynthesis and carbon sequestration, and gains in efficiency for LAI measurements are possible using remotely sensed imagery. However, the potential effects of complex topography on this measurement system are not well understood. Our objective was to understand how complex terrain and measurement aggregation influence the relationship between LAI and remotely sensed vegetation indices across a mountainous conifer forest. We identified NDVIc, a middle-infrared (MIR) correction to NDVI (Normalized Difference Vegetation Index), as the vegetation index providing the best prediction of effective plant area index (PAIe), used to approximate LAI. We tested formal hypotheses to identify how elevation and solar insolation gradients and spatial scale of measurement aggregation affected the PAIeNDVIc relationship and found that it changed across elevation at one spatial scale. Comparisons of NDVIc with NDVI revealed that vegetation index choice is important in complex terrain, and we concluded that the MIR correction improves the PAIeNDVI relationship by explaining variation related to solar insolation. Our results suggest that NDVIc calculated from Landsat ETM+ provides a practical estimate of PAIeacross our northern Idaho study area and potentially other conifer forests in complex terrain.
Incorporating average and maximum area restrictions in harvest scheduling models
Authors: Murray Alan T , Goycoolea Marcos , Weintraub Andrés
Published: March 2004

A major goal in natural resource management has long been balancing the multiple uses of forest lands. Timber harvesting remains an important component of natural resource utilization, but must be approached in such a way that recreational use, ecosystem dynamics, species survivability, and other considerations are not sacrificed. One way in which production impacts are mitigated in forest management is by restricting the spatial extent of harvesting activities in developed plans. Through the use of harvest scheduling optimization models, constraints can be structured and imposed to limit local area disturbance associated with harvesting to a stipulated maximum. This represents an approach for regulating impacts in an economically driven management setting. Harvest scheduling research has recognized the challenges in appropriately structuring maximum area restrictions in optimization models, but regulating average disturbance area size may also be desired. This paper develops a model formulation for imposing average and maximum area limits on local impacts in harvest scheduling that can be solved using exact techniques. Application results are presented that highlight the feasibility of this approach. Further, the associated tradeoffs that exist in modeling both average and maximum area restrictions simultaneously are illustrated.
Response of Gaultheria shallon and Epilobium angustifolium to large additions of nitrogen and phosphorus fertilizer
Authors: Bennett Jennifer N , Lapthorne Brent M , Blevins Leandra L , Prescott Cindy E
Published: March 2004

A study was established in coastal British Columbia to determine if repeated nitrogen (N) and phosphorus (P) fertilization negatively influences the reestablishment of salal (Gaultheria shallon Pursh) on cleared and burned cedarhemlock (Thuja plicata Donn ex D. Don  Tsuga heterophylla (Raf.) Sarg.) forests. Fertilizers were applied for 3 years, and the biomass of ground vegetation and conifer seedling survival and growth were measured. Salal biomass decreased with high levels of N application (1000 kg N/ha), but not when 400 kg P/ha was added with 1000 kg N/ha. The addition of 500 kg N/ha, with or without P, stimulated salal growth. The biomass of fireweed (Epilobium angusti folium L.) increased with the addition of N + P but not with N alone. In the high N and N + P treatments, conifer seedling survival and heights were reduced. These results confirm earlier reports that salal responds negatively to high N applications and that this negative response can be alleviated with simultaneous additions of P. The response of fireweed to N + P, but not to N alone, suggests that the abundance of this species is more indicative of P than N availability.
Stand composition and structure of the boreal mixedwood and epigaeic arthropods of the Ecosystem Management Emulating Natural Disturbance (EMEND) landbase in northwestern Alberta
Authors: Work Timothy T , Shorthouse David P , Spence John R , Volney W Jan A , Langor David
Published: March 2004

Conservation of biological diversity under the natural disturbance model of boreal forest management relies on the assumption that natural mosaics of stand composition and structure can be adequately recreated through forest management activities. Maintaining compositional and structural features that provide adequate habitat for species within managed stands is the basis of coarse-filter conservation strategies. Here we test the effect of stand composition and stand structure on the epigaeic arthropod fauna from four boreal mixedwood cover types in western Canada. We observed differences in epigaeic community composition and species-specific associations among each of the four cover types. Differences in the carabid fauna between cover types were defined by relative abundance of carabid species associated specifically with moss cover, forb cover, and of coarse woody material, rather than unique, stand-specific species compositions of the overstory. Cover-type differences were less apparent among the comparatively species-rich spider assemblages largely because of their low abundance in undisturbed stands. For the effective conservation of all species, our results suggest that coarse-filter management of mixedwood boreal forests must incorporate structural features beyond overstory canopy composition. Our analyses also suggest that activities directed at managing the amount of coarse woody material on the ground and understory plant composition, perhaps through variable retention harvesting, is a logical first step.
How long do Norway spruce snags stand? Evaluating four estimation methods
Authors: Storaunet Ken Olaf , Rolstad Jørund
Published: March 2004

We estimated time from death to fall (standing time) of Norway spruce (Picea abies (L.) Karst.) snags in a submountainous old-growth forest in south-central Norway, applying four calculation methods to 124 dendro chrono logically cross-dated still-standing snags and 64 fallen logs. The calculation methods consistently estimated expected standing time of snags at 2634 years, with a median of 1621 years and 20% of snags standing for >4858 years. The survival function from all methods took the approximate form of a negative exponential, with a 3%4% annual fall rate for snags. In the distribution of time since death, a small peak in dead trees 2030 years ago (late 1970s) coincides with a historic epidemic of bark beetles. The method using only time since death of still-standing snags appears to be the most feasible for estimating total standing time of snags in old-growth forests with constant tree mortality.
The responses of black spruce growth to an increased proportion of aspen in mixed stands
Authors: Légaré Sonia , Paré David , Bergeron Yves
Published: March 2004

In the southeastern boreal forest of Canada, the presence of mixed stands of black spruce (Picea mariana (Mill.) BSP) and trembling aspen (Populus tremuloides Michx.) growing in similar abiotic conditions offers the opportunity to study the influence of aspen on stand volume and spruce growth. A regression analysis performed on field data from the ministère des Ressources naturelles du Québec showed a significant relationship between the relative basal area of aspen (aspen relative basal area was determined by the ratio of aspen basal area to total basal area of the stand) and the total stand merchantable volume after accounting for stand density. However, the relationship between total black spruce volume and relative basal area of aspen was not significant, implying that the volume gain was, in fact, aspen fibre. The positive effects of aspen on black spruce DBH and height were only present when the proportion of aspen in the stand ranged between 0% and 41% of the total stand basal area. These results suggest that aspen uses a different niche than black spruce. Furthermore, the significant increase in black spruce dominant height along the aspen gradient suggests that aspen enhances soil fertility by its influence on nutrient availability. The management of mixed stands, which make up an important proportion on the landscape, offers an example as to how commercial management of the forest can be in agreement with ecosystem management.
Forest structure and composition at young fire and cut edges in black spruce boreal forest
Authors: Harper Karen A , Lesieur Daniel , Bergeron Yves , Drapeau Pierre
Published: March 2004

We compared structure and composition at forest edges created by wildfire and clear-cutting in black spruce (Picea mariana (Mill.) BSP) dominated boreal forest in northwestern Quebec. Forest structure and plant species composition were sampled along transects perpendicular to eight 3- to 4-year-old fire edges and eight 2- to 5-year-old cut edges. Significance of edge influence was assessed by comparing mean values at different distances from the edge to the range of variation in interior forest. The influence of clearcut edges was minimal, generally extending only 5 m from the edge, and included greater log density and different species composition, compared with interior forest. At fire edges, prominent responses to edge creation included increased snag density and lower moss cover, compared with interior forest, extending up to 40 m into the forest. This initial structural change was likely due to partial burning extending into the forest. Overall, fire edges had more snags and a different species composition than cut edges. Our hypothesis that edge influence is more extensive at fire edges than at cut edges was supported for overstory and understory structure, but not for species composition. We suggest that there is a need for management to consider the cumulative effect of the loss of fire edges on the landscape.
DYNAMIC STREAMS FOR EFFICIENT COMMUNICATIONS BETWEEN MIGRATING PROCESSES IN A CLUSTER
Authors: GALLARD PASCAL , MORIN CHRISTINE
Published: March 2004

This paper presents a communication system designed to allow efficient process migration in a cluster. The proposed system is generic enough to allow the migration of any kind of stream: socket, pipe, char devices. Communicating processes using IP or Unix sockets are transparently migrated with our mechanisms and they can still efficiently communicate after migration. The designed communication system is implemented as part of Kerrighed, a single system image operating system for a cluster based on Linux. Preliminary performance results are presented.
HIERARCHICAL PEER-TO-PEER SYSTEMS
Authors: GARCÉS-ERICE L. , BIERSACK E. W. , ROSS K. W. , FELBER P. A. , URVOY-KELLER G.
Published: March 2004

Structured peer-to-peer (P2P) lookup services organize peers into a flat overlay network and offer distributed hash table (DHT) functionality. Data is associated with keys and each peer is responsible for a subset of the keys. In hierarchical DHTs, peers are organized into groups, and each group has its autonomous intra-group overlay network and lookup service. Groups are organized in a top-level overlay network. To find a peer that is responsible for a key, the top-level overlay first determines the group responsible for the key; the responsible group then uses its intra-group overlay to determine the specific peer that is responsible for the key. We provide a general framework for hierarchical DHTs with scalable overlay management. We specifically study a two-tier hierarchy that uses Chord for the top level. Our analysis shows that by using the most reliable peers in the top level, the hierarchical design significantly reduces the expected number of hops. We also present a method to construct hierarchical DHTs that map well to the Internet topology and achieve short intra-group communication delay. The results demonstrate the feasibility of locality-based peer groups, which allow P2P systems to take full advantage of the hierarchical design.
Hypoxia-induced pulmonary artery adventitial remodeling and neovascularization: contribution of progenitor cells
Authors: Davie Neil J. , Crossno Joseph T. , Frid Maria G. , Hofmeister Stephen E. , Reeves John T. , Hyde Dallas M. , Carpenter Todd C. , Brunetti Jacqueline A. , McNiece Ian K. , Stenmark Kurt R.
Published: March 2004

Information is rapidly emerging regarding the important role of the arterial vasa vasorum in a variety of systemic vascular diseases. In addition, increasing evidence suggests that progenitor cells of bone marrow (BM) origin may contribute to postnatal neovascularization and/or vascular wall thickening that is characteristic in some forms of systemic vascular disease. Little is known regarding postnatal vasa formation and the role of BM-derived progenitor cells in the setting of pulmonary hypertension (PH). We sought to determine the effects of chronic hypoxia on the density of vasa vasorum in the pulmonary artery and to evaluate if BM-derived progenitor cells contribute to the increased vessel wall mass in a bovine model of hypoxia-induced PH. Quantitative morphometric analyses of lung tissue from normoxic and hypoxic calves revealed that hypoxia results in a dramatic expansion of the pulmonary artery adventitial vasa vasorum. Flow cytometric analysis demonstrated that cells expressing the transmembrane tyrosine kinase receptor for stem cell factor, c-kit, are mobilized from the BM in the circulation in response to hypoxia. Immunohistochemistry revealed an increase in the expression of c- kit+cells together with vascular endothelial growth factor, fibronectin, and thrombin in the hypoxia-induced remodeled pulmonary artery vessel wall. Circulating mononuclear cells isolated from neonatal calves exposed to hypoxia were found to differentiate into endothelial and smooth muscle cell phenotypes depending on culture conditions. From these observations, we suggest that the vasa vasorum and circulating progenitor cells could be involved in vessel wall thickening in the setting of hypoxia-induced PH.
p38mapk and MEK1/2 inhibition contribute to cellular oxidant injury after hypoxia
Authors: Powell Charles S. , Wright Marcienne M. , Jackson Robert M.
Published: March 2004

Lung epithelial cells produce increased reactive oxygen species (ROS) after hypoxia exposure, and they are more susceptible after hypoxia to injury by agents that generate superoxide [[Formula: see text]; e.g., 2,3-dimethoxy-1,4-naphthoquinone (DMNQ)]. Cellular GSH and MnSOD both decrease in hypoxic lung epithelial cells, altering the redox state. Because ROS participate in signaling pathways involved in cell death or survival, we tested the hypothesis that mitogen-activated protein kinases (MAPK) were involved in a protective response against cellular injury during reoxygenation. Human lung epithelial A549 cells were incubated in hypoxia (<1% O2 for 24 h) and then reoxygenated by return to air. p38mapk and MKK3 phosphorylation both decreased after hypoxia. During reoxygenation, cells were incubated with DMNQ (0–50 μM), a redox cycling quinone that produces [Formula: see text]. Hypoxia preexposure significantly increased epithelial cell lysis resulting from DMNQ. Addition of the p38mapk inhibitors SB-202190 or SB-203580 markedly increased cytotoxicity, as did the mitogen/extracellular signal-regulated kinase (MEK) 1/2 inhibitor PD-98059 (all 10 μM), suggesting a protective effect of downstream molecules activated by the kinases. Transfection of A549 cells with a dominant active MKK3 plasmid (MKK3[Glu]) partially inhibited cytolysis resulting from DMNQ, whereas the inactive MKK3 plasmid (MKK3[Ala]) had less evident protective effects. Stress-related signaling pathways in epithelial cells are modulated by hypoxia and confer protection from reoxygenation, since hypoxia and chemical inhibition of p38mapk and MEK1/2 similarly increase cytolysis resulting from [Formula: see text].
Molecular phenotype of airway side population cells
Authors: Giangreco Adam , Shen Hongmei , Reynolds Susan D. , Stripp Barry R.
Published: March 2004

Lung epithelial-specific stem cells have been localized to discrete microenvironments throughout the adult conducting airway. Properties of these cells include pollutant resistance, multipotent differentiation, and infrequent proliferation. Goals of the present study were to use Hoechst 33342 efflux, a property of stem cells in other tissues, to purify and further characterize airway stem cells. Hoechst 33342 effluxing lung cells were identified as a verapamil-sensitive side population by flow cytometry. Lung side population cells were further subdivided on the basis of hematopoietic (CD45 positive) or nonhematopoietic (CD45 negative) origin. Nonhematopoietic side population cells were enriched for stem cell antigen-1 reactivity and expressed molecular markers specific to both airway and mesenchymal lineages. Analysis of the molecular phenotype of airway-derived side population cells indicates that they are similar to neuroepithelial body-associated variant Clara cells. Taken together, these data suggest that the nonhematopoietic side population isolated from lung is enriched for previously identified airway stem cells.