bluuebunny/crossref_metadata_2025 huggingface dataset:
CONTEXTUALIZING LEARNING OBJECTS USING ONTOLOGIES
Authors: Mohammed Phaedra , Mohan Permanand
Published: July 2007

Educational research over the past three years has intensified such that the context of learning resources needs to be properly modeled. Many researchers have described and even mandated the use of ontologies in the research being conducted, yet the process of actually connecting one or more ontologies to a learning object has not been extensively discussed. This paper describes a practical model for associating multiple ontologies with learning objects while making full use of the IEEE LOM specification. The model categorizes these ontologies according to five major categories of context based on the most popular fields of study actively being pursued by the educational research community: Thematic context, Pedagogical context, Learner context, Organizational context, and Historical/Statistical context.
Analysis of Thermally Expandable Flexible Fluidic Thin-Film Channels
Authors: Khaled A.-R. A. , Vafai K.
Published: July 2007

Heat transfer inside thermally expandable and flexible fluidic thin-film channels is analyzed in this work. Two categories are analyzed: the first category is when the upper plate of the thin film is mobile and flexible, and the second is when the side plates of the thin film are flexible and mobile. The expansion in the thin-film heights (category I) or widths (category II) are linearly related to the local fluid pressure and the local temperature of the heated plate based on the principles of linear elasticity and constant volumetric thermal expansion coefficient. The governing Reynolds, momentum, and energy equations are properly nondimensionalized and solved numerically using an implicit method. The Peclet number, stiffness parameter, thermal expansion parameter, and aspect ratio are found to be the main controlling parameters. It is found that thermally expandable flexible thin films that belong to category I can produce significant increase in cooling as the heating load increases, especially when operated at lower Peclet numbers, whereas the cooling effect for those that belong to category II is almost unaffected by the expansion. This work paves the way to practically utilize thermally expandable flexible thin films, especially in MEMS and electronic cooling applications.
Direct Numerical Simulation of Heat Transfer in Converging–Diverging Wavy Channels
Authors: Stalio E. , Piller M.
Published: July 2007

Corrugated walls are widely used as passive devices for heat and mass transfer enhancement; they are most effective when operated at transitional and turbulent Reynolds numbers. In the present study, direct numerical simulation is used to investigate the unsteady forced convection in sinusoidal, symmetric wavy channels. A novel numerical method is employed for the simulations; it is meant for fully developed flows in periodic ducts of prescribed wall temperature. The algorithm is free of iterative procedures; it accounts for the effects of streamwise diffusion and can be used for unsteady problems. Results of two simulations in the transitional regime for Reynolds numbers based on average duct height and average velocity of Re=481 and Re=872 are reported. Time averaged and instantaneous velocity and temperature fields together with second-order statistics are interpreted in order to describe the mechanism associated with heat transfer augmentation. Heat flux distributions locate the most active areas in heat transfer and reveal the effects of convective mixing. Slanted traveling waves of high temperature are identified; peak values of Nusselt number are attained when the high-temperature fluid of the waves reaches the converging walls.
Heat Exchanger Design Methodology for Electronic Heat Sinks
Authors: Webb Ralph L.
Published: July 2007

This paper discusses the “inlet temperature difference” (ITD) based heat-exchanger (and its variants) design methodology frequently used by designers of electronic heat sinks. This is at variance with the accepted methodology recommended in standard heat-exchanger textbooks—the “log-mean temperature difference,” or the equivalent ε-NTU design method. The purpose of this paper is to evaluate and discuss the ITD based design methodology. The paper shows that the ITD based method is an approximation at best. Variants of the method can lead to either under- or overprediction of the heat transfer rate. Its shortcomings are evaluated and designers are directed to the well established and accepted design methodology.
Numerical Study of Single Bubble Dynamics During Flow Boiling
Authors: Li Ding , Dhir Vijay K.
Published: July 2007

Three-dimensional numerical simulation of single bubble dynamics during nucleate flow boiling is performed in this work. The range of bulk liquid velocities investigated is from 0.076to0.23m∕s. The surface orientations at earth normal gravity are varied from an upward facing horizontal surface to vertical through 30, 45, and 60deg. The gravity levels on an upward facing horizontal surface are varied from 1.0ge to 0.0001ge. Continuity, momentum, and energy equations are solved by finite difference method and the level set method is used to capture the liquid-vapor interface. Heat transfer within the liquid micro layer is included in this model. The numerical results have been compared with data from experiments. The results show that the bulk flow velocity, heater surface orientation, and gravity levels influence the bubble dynamics.
Checkers Is Solved
Authors: Schaeffer Jonathan , Burch Neil , Björnsson Yngvi , Kishimoto Akihiro , Müller Martin , Lake Robert , Lu Paul , Sutphen Steve
Published: July 2007

The game of checkers has roughly 500 billion billion possible positions (5 × 10
20
). The task of solving the game, determining the final result in a game with no mistakes made by either player, is daunting. Since 1989, almost continuously, dozens of computers have been working on solving checkers, applying state-of-the-art artificial intelligence techniques to the proving process. This paper announces that checkers is now solved: Perfect play by both sides leads to a draw. This is the most challenging popular game to be solved to date, roughly one million times as complex as Connect Four. Artificial intelligence technology has been used to generate strong heuristic-based game-playing programs, such as Deep Blue for chess. Solving a game takes this to the next level by replacing the heuristics with perfection.
Seasonal Dynamics of Arbuscular Mycorrhizal Fungal Communities in Roots in a Seminatural Grassland
Authors: Santos-González Juan C. , Finlay Roger D. , Tehler Anders
Published: July 2007

Symbiotic arbuscular mycorrhizal fungi (AMF) have been shown to influence both the diversity and productivity of grassland plant communities. These effects have been postulated to depend on the differential effects of individual mycorrhizal taxa on different plant species; however, so far there are few detailed studies of the dynamics of AMF colonization of different plant species. In this study, we characterized the communities of AMF colonizing the roots of two plant species,
Prunella vulgaris
and
Antennaria dioica
, in a Swedish seminatural grassland at different times of the year. The AMF small subunit rRNA genes were subjected to PCR, cloning, sequencing, and phylogenetic analysis. Nineteen discrete sequence types belonging to
Glomus
groups A and B and to the genus
Acaulospora
were distinguished. No significant seasonal changes in the species compositions of the AMF communities as a whole were observed. However, the two plant species hosted significantly different AMF communities.
P. vulgaris
hosted a rich AMF community throughout the entire growing season. The presence of AMF in
A. dioica
decreased dramatically in autumn, while an increased presence of
Ascomycetes
species was detected.
Selection and Characterization of Cyanophage Resistance in Marine
Synechococcus
Strains
Authors: Stoddard Lauren I. , Martiny Jennifer B. H. , Marston Marcia F.
Published: July 2007

Marine viruses are an important component of the microbial food web, influencing microbial diversity and contributing to bacterial mortality rates. Resistance to cooccurring cyanophages has been reported for natural communities of
Synechococcus
spp.; however, little is known about the nature of this resistance. This study examined the patterns of infectivity among cyanophage isolates and unicellular marine cyanobacteria (
Synechococcus
spp.). We selected for phage-resistant
Synechococcus
mutants, examined the mechanisms of phage resistance, and determined the extent of cross-resistance to other phages. Four strains of
Synechococcus
spp. (WH7803, WH8018, WH8012, and WH8101) and 32 previously isolated cyanomyophages were used to select for phage resistance. Phage-resistant
Synechococcus
mutants were recovered from 50 of the 101 susceptible phage-host pairs, and 23 of these strains were further characterized. Adsorption kinetic assays indicate that resistance is likely due to changes in host receptor sites that limit viral attachment. Our results also suggest that receptor mutations conferring this resistance are diverse. Nevertheless, selection for resistance to one phage frequently resulted in cross-resistance to other phages. On average, phage-resistant
Synechococcus
strains became resistant to eight other cyanophages; however, there was no significant correlation between the genetic similarity of the phages (based on
g20
sequences) and cross-resistance. Likewise, host
Synechococcus
DNA-dependent RNA polymerase (
rpoC1
) genotypes could not be used to predict sensitivities to phages. The potential for the rapid evolution of multiple phage resistance may influence the population dynamics and diversity of both
Synechococcus
and cyanophages in marine waters.
Pathotyping
Escherichia coli
by Using Miniaturized DNA Microarrays
Authors: Anjum Muna F. , Mafura Muriel , Slickers Peter , Ballmer Karin , Kuhnert Peter , Woodward Martin J. , Ehricht Ralf
Published: July 2007

The detection of virulence determinants harbored by pathogenic
Escherichia coli
is important for establishing the pathotype responsible for infection. A sensitive and specific miniaturized virulence microarray containing 60 oligonucleotide probes was developed. It detected six
E. coli
pathotypes and will be suitable in the future for high-throughput use.
Changes in the Catalytic Properties of
Pyrococcus furiosus
Thermostable Amylase by Mutagenesis of the Substrate Binding Sites
Authors: Yang Sung-Jae , Min Byoung-Chul , Kim Young-Wan , Jang Sang-Mok , Lee Byong-Hoon , Park Kwan-Hwa
Published: July 2007

Pyrococcus furiosus
thermostable amylase (TA) is a cyclodextrin (CD)-degrading enzyme with a high preference for CDs over maltooligosaccharides. In this study, we investigated the roles of four residues (His414, Gly415, Met439, and Asp440) in the function of
P. furiosus
TA by using site-directed mutagenesis and kinetic analysis. A variant form of
P. furiosus
TA containing two mutations (H414N and G415E) exhibited strongly enhanced α-(1,4)-transglycosylation activity, resulting in the production of a series of maltooligosaccharides that were longer than the initial substrates. In contrast, the variant enzymes with single mutations (H414N or G415E) showed a substrate preference similar to that of the wild-type enzyme. Other mutations (M439W and D440H) reversed the substrate preference of
P. furiosus
TA from CDs to maltooligosaccharides. Relative substrate preferences for maltoheptaose over β-CD, calculated by comparing
k
cat
/

K
m

ratios, of 1, 8, and 26 for wild-type
P. furiosus
TA,
P. furiosus
TA with D440H, and
P. furiosus
TA with M439W and D440H, respectively, were found. Our results suggest that His414, Gly415, Met439, and Asp440 play important roles in substrate recognition and transglycosylation. Therefore, this study provides information useful in engineering glycoside hydrolase family 13 enzymes.
Relative Abundances of Proteobacterial Membrane-Bound and Periplasmic Nitrate Reductases in Selected Environments
Authors: Bru D. , Sarr A. , Philippot L.
Published: July 2007

Dissimilatory nitrate reduction is catalyzed by a membrane-bound and a periplasmic nitrate reductase. We set up a real-time PCR assay to quantify these two enzymes, using the
narG
and
napA
genes, encoding the catalytic subunits of the two types of nitrate reductases, as molecular markers. The
narG
and
napA
gene copy numbers in DNA extracted from 18 different environments showed high variations, with most numbers ranging from 2 × 10
2
to 6.8 × 10
4
copies per ng of DNA. This study provides evidence that, in soil samples, the number of proteobacteria carrying the
napA
gene is often as high as that of proteobacteria carrying the
narG
gene. The high correlation observed between
narG
and
napA
gene copy numbers in soils suggests that the ecological roles of the corresponding enzymes might be linked.
Transcription and Regulation of the Bidirectional Hydrogenase in the Cyanobacterium
Nostoc
sp. Strain PCC 7120
Authors: Sjöholm Johannes , Oliveira Paulo , Lindblad Peter
Published: July 2007

The filamentous, heterocystous cyanobacterium
Nostoc
sp. strain PCC 7120 (
Anabaena
sp. strain PCC 7120) possesses an uptake hydrogenase and a bidirectional enzyme, the latter being capable of catalyzing both H
2
production and evolution. The completely sequenced genome of
Nostoc
sp. strain PCC 7120 reveals that the five structural genes encoding the bidirectional hydrogenase (
hoxEFUYH
) are separated in two clusters at a distance of approximately 8.8 kb. The transcription of the
hox
genes was examined under nitrogen-fixing conditions, and the results demonstrate that the cluster containing
hoxE
and
hoxF
can be transcribed as one polycistronic unit together with the open reading frame alr0750. The second cluster, containing
hoxU
,
hoxY
, and
hoxH
, is transcribed together with alr0763 and alr0765, located between the
hox
genes. Moreover, alr0760 and alr0761 form an additional larger operon. Nevertheless, Northern blot hybridizations revealed a rather complex transcription pattern in which the different
hox
genes are expressed differently. Transcriptional start points (TSPs) were identified 66 and 57 bp upstream from the start codon of alr0750 and
hoxU
, respectively. The transcriptions of the two clusters containing the
hox
genes are both induced under anaerobic conditions concomitantly with the induction of a higher level of hydrogenase activity. An additional TSP, within the annotated alr0760, 244 bp downstream from the suggested translation start codon, was identified. Electrophoretic mobility shift assays with purified LexA from
Nostoc
sp. strain PCC 7120 demonstrated specific interactions between the transcriptional regulator and both
hox
promoter regions. However, when LexA from
Synechocystis
sp. strain PCC 6803 was used, the purified protein interacted only with the promoter region of the alr0750-
hoxE
-
hoxF
operon. A search of the whole
Nostoc
sp. strain PCC 7120 genome demonstrated the presence of 216 putative LexA binding sites in total, including
recA
and
recF
. This indicates that, in addition to the bidirectional hydrogenase gene, a number of other genes, including open reading frames connected to DNA replication, recombination, and repair, may be part of the LexA regulatory network in
Nostoc
sp. strain PCC 7120.
Quantification of 2,4-Diacetylphloroglucinol-Producing
Pseudomonas fluorescens
Strains in the Plant Rhizosphere by Real-Time PCR
Authors: Mavrodi Olga V. , Mavrodi Dmitri V. , Thomashow Linda S. , Weller David M.
Published: July 2007

A real-time PCR SYBR green assay was developed to quantify populations of 2,4-diacetylphloroglucinol (2,4-DAPG)-producing (
phlD
+
) strains of
Pseudomonas fluorescens
in soil and the rhizosphere. Primers were designed and PCR conditions were optimized to specifically amplify the
phlD
gene from four different genotypes of
phlD
+
P. fluorescens
. Using purified genomic DNA and genomic DNA extracted from washes of wheat roots spiked with bacteria, standard curves relating the threshold cycles (

C
T

s) and copies of the
phlD
gene were generated for
P. fluorescens
strains belonging to genotypes A (Pf-5), B (Q2-87), D (Q8r1-96 and FTAD1R34), and I (FTAD1R36). The detection limits of the optimized real-time PCR assay were 60 to 600 fg (8 to 80 CFU) for genomic DNA isolated from pure cultures of
P. fluorescens
and 600 fg to 6.0 pg (80 to 800 CFU, corresponding to log 4 to 5
phlD
+
strain CFU/rhizosphere) for bacterial DNA extracted from plant root washes. The real-time PCR assay was utilized to quantify
phlD
+
pseudomonads in the wheat rhizosphere. Regression analysis of population densities detected by real-time PCR and by a previously described
phlD
-specific PCR-based dilution endpoint assay indicated a significant linear relationship (
P
= 0.0016,
r
2
= 0.2). Validation of real-time PCR assays with environmental samples was performed with two different soils and demonstrated the detection of more than one genotype in Quincy take-all decline soil. The greatest advantage of the developed real-time PCR is culture independence, which allows determination of population densities and the genotype composition of 2,4-DAPG producers directly from the plant rhizospheres and soil.
Chlamydial CT441 Is a PDZ Domain-Containing Tail-Specific Protease That Interferes with the NF-κB Pathway of Immune Response
Authors: Lad Sonya P. , Yang Guang , Scott David A. , Wang Guizhen , Nair Priyanka , Mathison John , Reddy Vijay S. , Li Erguang
Published: July 2007

Chlamydia
species are bacterial pathogens that affect over 140 million individuals worldwide. Ocular infection by
Chlamydia trachomatis
is the leading cause of preventable blindness, and urogenital tract infection by
Chlamydia
causes sexually transmitted disease. As obligate intracellular organisms,
Chlamydia
species have evolved mechanisms to evade the host immune system, including the degradation of the transcription factors regulatory factor X5 and upstream stimulation factor 1, which are required for the expression of major histocompatibility complex molecules I and II by CPAF and cleavage of p65 of the NF-κB pathway by the encoded CT441 protein. Here, we report the characterization of CT441 as a tail-specific protease. CT441 contains a PDZ domain of protein-protein interactions and a Ser/Lys dyad catalytic unit. Mutation at either Ser455 or Lys481 in the active site ablated CT441 activity of p65 cleavage. In addition, we found that the production of CT441 Tsp, which was detected at the middle and late stages of an infection, correlated with p65 cleavage activity. In addition to high homology, human and mouse p65 proteins also contain an identical C-terminal tail of 22 amino acid (aa) residues. However, only human p65 was susceptible to cleavage. Using molecular biology approaches, we mapped the p65 cleavage site(s) to a region that differs from that of mouse p65 by 6 aa residues. Additionally, the substitution of T352 with a proline inhibited p65 cleavage. Together, the study demonstrates that CT441 is a tail-specific protease that is capable of interfering with the NF-κB pathway of host antimicrobial and inflammatory responses.
SpxB Is a Suicide Gene ofStreptococcus pneumoniaeand Confers a Selective Advantage in an In Vivo Competitive Colonization Model
Authors: Regev-Yochay Gili , Trzcinski Krzysztof , Thompson Claudette M. , Lipsitch Marc , Malley Richard
Published: July 2007

The human bacterial pathogenStreptococcus pneumoniaedies spontaneously upon reaching stationary phase. The extent ofS. pneumoniaedeath at stationary phase is unusual in bacteria and has been conventionally attributed to autolysis by the LytA amidase. In this study, we show that spontaneous pneumococcal death is due to hydrogen peroxide (H2O2), not LytA, and that the gene responsible for H2O2production (spxB) also confers a survival advantage in colonization. Survival ofS. pneumoniaein stationary phase was significantly prolonged by eliminating H2O2in any of three ways: chemically by supplementing the media with catalase, metabolically by growing the bacteria under anaerobic conditions, or genetically by constructing ΔspxBmutants that do not produce H2O2. Likewise, addition of H2O2to exponentially growingS. pneumoniaeresulted in a death rate similar to that of cells in stationary phase. While ΔlytAmutants did not lyse at stationary phase, they died at a rate similar to that of the wild-type strain. Furthermore, we show that the death process induced by H2O2has features of apoptosis, as evidenced by increased annexin V staining, decreased DNA content, and appearance as assessed by transmission electron microscopy. Finally, in an in vivo rat model of competitive colonization, the presence ofspxBconferred a selective advantage over the ΔspxBmutant, suggesting an explanation for the persistence of this gene. We conclude that a suicide gene of pneumococcus isspxB, which induces an apoptosis-like death in pneumococci and confers a selective advantage in nasopharyngeal cocolonization.
Flow dynamics and bedload sediment transport around paired deflectors for fish habitat enhancement: a field study in the Nicolet River
Authors: Carré David M , Biron Pascale M , Gaskin Susan J
Published: July 2007

Schemes to restore fish habitat in rivers often involve installing instream structures such as current deflectors to create and maintain riffle-pool sequences. However, there is a lack of field studies on the impact of these structures on flow dynamics and bed topography. The objective of this research is to characterize flow dynamics and sediment transport around paired deflectors used to enhance fish habitat in the Nicolet River, Quebec. Bed and bank topography surveys were taken with a total station, and velocity and bed shear stress estimates were obtained from an acoustic doppler velocimeter. Bedload sediment transport was assessed by two methods: tracer rocks (painted "particles" and passive integrated transponder tags) and sediment traps. Results show marked differences in bedload sediment transport patterns between the left bank and the right bank downstream of the deflectors. This is surprising considering that paired deflectors should produce a relatively symmetrical disruption to the flow field on each side. More high-flow dynamics data during overtopping conditions are required to understand the complex interactions between these instream structures and bedload transport. Key words: stream restoration, pool, bedload transport, radio frequency identification (RFID), passive integrated transponder (PIT) tags, fieldwork, deflectors, fish habitat.
Investigation of the effects of different polymer-modified asphalt cements on asphalt mixes at low temperature
Authors: Kandil K , Abd El Halim A O , Hassan Y , Mostafa A
Published: July 2007

The extreme environmental conditions in Canada require the use of asphalt cement that can provide a high resistance to low-temperature cracking during the winter season and a high resistance to rutting due to the elevated temperatures in the summer. Earlier studies showed that such desired improvements in the quality of asphalt cement could be achieved using polymer-modified asphalt (PMA) cement. This paper presents a three-phase experimental program that was carried out to evaluate the expected performance of asphalt concrete mixtures with PMA compared to asphalt concrete mixtures with conventional and air-oxidized asphalt binders. The results of this study show that PMA in asphalt concrete mixes would significantly improve the resistance to cracking (loading and low-temperature). Key words: asphalt mixtures, polymer-modified asphalt, conventional asphalt cement, air-oxidized asphalt, testing.
Flexural behaviour of reinforced or prestressed concrete beams including strengthening with prestressed carbon fibre reinforced polymer sheets: application of a fracture mechanics approach
Authors: Kim Yail J , Green Mark F , Wight R Gordon
Published: July 2007

This paper describes the application of a fracture mechanics model (Hillerborg 1990) to concrete structures, including strengthening with prestressed carbon fibre reinforced polymer (CFRP) sheets. One benefit of the proposed fracture mechanics model, consisting of a unique combined stress–strain response of concrete, is that it includes the size effect of reinforced concrete beams; however, its application and validation have not been fully investigated. The proposed model is reviewed and further developed to cover prestressed concrete beams including a beam strengthened with a prestressed CFRP sheet. To evaluate the model, various approaches such as finite element analysis, a strength-based model, a conventional design method, and experimental results are compared with the fracture mechanics model. The size-dependent parameter (ε1) significantly affects the predicted behaviour of reinforced or prestressed concrete beams, depending on the contribution of reinforcement. Based on the current assessment, ε1 = 0.005 is recommended as an upper limit for normal strength concrete.Key words: carbon fibre reinforced polymer sheet, flexure, fracture mechanics, prestressed concrete beam, reinforced concrete beam, strengthening, size effect.
Batch studies of lead adsorption from a multi-component aqueous solution onto Atlantic cod fish scale (Gadus morhua) substrate
Authors: Basu A , Rahaman M S , Mustafiz S , Islam M R
Published: July 2007

Aqueous streams often posses several contaminants that are of environmental concerns. Removing these contaminants from the multi-component phases is a challenging task. In this study, the multi-component (combination of lead and arsenic ions) batch adsorption results are analyzed with respect to initial concentrations of the contaminants (lead: 2.5, 10, and 40 mg/L; arsenic: 350 and 1000 μg/L) and pH variations (pH value of 4, 7, 9, and 11) of the bulk phase. The adsorbent selected for this research is Atlantic cod (Gadus morhua) fish scale. A general trend of reduced lead adsorptivity with increasing arsenic concentration is observed at the lower concentration of 2.5 mg/L of the heavy metal cation. The decrease in lead to arsenic concentration ratio in the bulk phase is correlated with an increase in "electrostatic attractions" or with "ion pair bridging" by the arsenic species on lead ions. However, at higher lead ion concentrations of 10 ppm and 40 ppm, the effect of arsenic on lead adsorption is insignificant.Key words: adsorption, arsenic, Atlantic cod fish scale, bio-sorption, lead, concentration ratio.
Oxydation des isomères de dichlorobenzène à l'aide du persulfate de sodium soumis à une activation thermique
Authors: Bougie Stéphanie , Dubé Jean-Sébastien
Published: July 2007

The chemical oxidation of a recalcitrant molecule, dichlorobenzene, with thermally activated persulfate was studied in an aqueous medium and in soil slurry (10% total solids). The use of persulfate was investigated to provide additional knowledge on its use in soil remediation. In an aqueous medium, a complete degradation of dichlorobenzene was observed at 50 and 60 ºC for a reaction time of 6 h. In soil slurry, a degradation of 90% and 100% was observed after 6 h at 50 and 60 ºC, respectively. At 40 ºC, the degradation was 64% in an aqueous medium and 26% in soil slurry. In both media, the activation energy of the reaction was 115 and 153 kJ/mol, respectively. It is more efficient to increase the activation temperature in soil slurry than in an aqueous medium. Key words: dichlorobenzene, persulfate, thermal activation, sulphate free radical, chemical oxidation, kinetics.
Western Spruce Budworm Damage Affects Form and Height Growth of Western Larch
Authors: Schmidt Wyman C. , Fellin David G.
Published: July 2007

An unusual feeding behavior of the western spruce budworm (Choristoneuraoccidentalis Freeman) reduced height growth and deformed young western larch (Larixoccidentalis Nutt.). On western larch, budworm larvae did not confine their feeding to foliage, their usual diet on other conifers; they also fed on and severed stems of current-year terminal and lateral shoots. A 5-year study in young larch stands showed that: (1) amount and severity of budworm damage increased annually, (2) all trees were damaged sometime during the study, (3) severance of the terminal shoot was the most serious type of budworm damage to larch, (4) severances reduced net height growth at least one-fourth and resulted in forked, bushy-topped trees, and (5) specific forks in the tree did not persist more than 5 years because of the strong apical dominance characteristic of larch.
Predictability of Shoot Length from Bud Size in Pinusresinosa Ait.
Authors: Kozlowski T. T. , Torrie J. H. , Marshall P. E.
Published: July 2007

Bud diameter, bud length, and shoot length varied widely in different shoot locations of 8-year-old Pinusresinosa trees. Over all locations and shoots within each tree, bud diameter and bud length, bud diameter and shoot length, and bud length and shoot length were highly correlated. Bud length was a better index than bud diameter of final shoot length. Over all trees and shoots within each location, the correlations between (1) bud diameter and bud length, (2) bud diameter and shoot length, or (3) bud length and shoot length were higher in upper whorl branches than in the terminal leader. Bud diameter and bud length were better indicators of shoot growth for upper whorl branches than for lower whorl branches or the terminal leader.
Canker of Dwarf Mistletoe Swellings on Western Hemlock Caused by Nectriafuckeliana var. macrospora
Authors: Funk A. , Smith R. B. , Baranyay J. A.
Published: July 2007

Nectriafuckeliana Booth var. macrospora (Wr.) Booth was commonly associated with open, resinous cankers of dwarf mistletoe swellings of western hemlock (Tsugaheterophylla (Raf.) Sarg.) in British Columbia, Canada. Pathogenicity of the fungus was proved by artificial inoculation and reisolation from cankered tissues. Cankers substantially reduced dwarf mistletoe reproduction.
Patterns of Annual Xylem Increment Integrated by Contour Presentation
Authors: Fayle D. C. F.
Published: July 2007

A functional method of bringing together the patterns in the annual increment of wood in the stem and root of a tree is presented and related to the analyses of Duff and Nolan. Alternative terms for the three growth analysis sequences of these authors are suggested. The contour presentation described provides a good visual construct, useful for comparative purposes, of the space–time relationships of the growth layer during the development of a tree.
The Movement of Dye Solution in Dwarf Mistletoe-infected Black Spruce Trees
Authors: Tainter F. H. , French D. W.
Published: July 2007

Upward movement of acid fuchsin dye solution in dwarf mistletoe-infected black spruce trees generally occurred in a helical pattern. In seven of ten trees the dye ascended in a counterclockwise direction around the axis of the tree. All trees showed wide variation in direction of ascent, in some cases the dye column reversed direction of ascent partially up the bole. In some instances the witches' brooms apparently attracted the dye.
Effects of controlled-release fertilizers on the shoot and root development of Douglas-fir seedlings
Authors: Carlson W. C. , Preisig C. L.
Published: July 2007

Controlled-release fertilizers, applied to the root zone of 1-0 plug Douglas-fir (Pseudotsugamenziesii Mirb. Franco) seedlings at planting, stimulated shoot and root growth in the following two growing seasons. Stem unit length was increased in the first growth flush after treatment, and a higher proportion of fertilized seedlings had a second growth flush that year. Fertilizing increased the number of needle primordia formed in the overwintered bud in the late summer and fall of the 1st year after treatment and increased the number of lateral buds formed the following spring, but did not affect the length of stem units elongated in the first growth flush of the 2nd year after treatment. Shoot–root ratio was not altered abnormally by fertilizing. Fertilizing increased the number and in some cases the diameter of lateral roots in the root system. Position of fertilizer placement did not alter root system symmetry in terms of the distribution of numbers of roots over 12 root zones.
Container- and nursery-grown black oak seedlings inoculated with Pisolithustinctorius: growth and ectomycorrhizal development during seedling production period
Authors: Dixon R. K. , Wright G. M. , Garrett H. E. , Cox G. S. , Johnson P. S. , Sander I. L.
Published: July 2007

Vegetative mycelial inoculum of Pisolithustinctorius was used to inoculate black oak (Quercusvelutina Lam.) seedlings grown in containers in a greenhouse and in a fumigated soil in a southern Missouri nursery. Evaluations of seedlings in the greenhouse and the nursery at the end of the first growing season revealed that Pisolithus formed ectomycorrhizae on approximately 40% of the lateral roots. In the nursery, seedling dry weight, shoot length, root collar diameter, and leaf area were significantly greater for inoculated seedlings than for noninoculated control seedlings. For container-grown seedlings, total dry weight, root dry weight, and leaf surface area were significantly increased by inoculation with Pisolithus. These results demonstrate that Pisolithus can be artifically introduced into fumigated nursery soil and sterile growth medium of containers and form ectomycorrhizae on black oak seedlings under greenhouse and nursery conditions.
Snowmelt modeling in a balsam fir forest: comparison between an energy balance model and other simplified models
Authors: Prévost Marcel , Barry Richard , Stein Jean , Plamondon André P.
Published: July 2007

This study compares snowmelt models and determines the relative importance of the meteorological parameters affecting snowmelt during the 1985, 1986, and 1987 melt seasons in a dense balsam fir stand in Laurentide forest, 80 km north of the city of Québec. Net all-wave radiation, air temperature, wind speed, relative humidity, and rainfall were correlated with meltwater that reached the base of the snow cover as measured with a 20-m2 snow lysimeter. The estimation of energy balance components of the snow cover during the snowmelt period showed that while solar radiation absorption dominated, turbulent transfers as well as heat exchanges with ground and rain were negligible. The temperature index model SNOW-17 yielded predictions of snow cover outflow as accurately as the energy balance model, both explaining 64% of hourly outflow variation and more than 85% of daily outflow variation. Single meteorological parameters usually explained less than 25% of the hourly melt because of the meltwater transmission lag through the snowpack. On a daily basis, the relationships using air temperature or net all-wave radiation as sole index both explained nearly 70% of snowmelt outflow for the same period. Combining these two parameters with rainfall in the same equation increased the explained variance to 85%.
Lightning-ignited forest fires in northwestern Ontario
Authors: Flannigan M. D. , Wotton B. M.
Published: July 2007

This study investigates the relationship between lightning activity and the occurrence of lightning-ignited forest fires in the Northwestern Region of Ontario. We found that the Duff Moisture Code (a component of the Fire Weather Index System) and the multiplicity of the negative lightning discharges were the most important variables for estimating the number of lightning-ignited fires on a daily basis for Universal Transverse Mercator zone15 in Ontario. Also, the results indicate that negative lightning ignited more fires than positive lightning discharges, which is contrary to popular belief. Nearly 50% of the variance in the forest fire occurrence data was explained using linear stepwise regression. Future work will focus on finer temporal and spatial scales.
Ethylene and ethane evolution during cold acclimation and deacclimation of ponderosa pine
Authors: Burr Karen E. , Wallner Stephen J. , Tinus Richard W.
Published: July 2007

Greenhouse container-grown ponderosa pine (Pinusponderosa var. scopulorum Engelm.) were cold acclimated and deacclimated in growth chambers during a 19-week regime. Seedling cold hardiness, bud dormancy, and ethylene and ethane evolution from excised needles were measured weekly. Ethylene and ethane evolution and the ethane/ethylene ratio declined from bud set to bud break and did not parallel changes in cold hardiness. Large standard errors of the ethylene evolution means made detecting statistical differences over time difficult. Significant deviations in the ethane evolution means were observed, however, and indicated a sharp decrease and recovery at the start of cold acclimation and a peak at the start of deacclimation. The ethane/ethylene ratio accentuated the declining trend from bud set to bud break and the two sharp deviations in the trend at the start of acclimation and deacclimation.
Carbohydrate changes in shortleaf pine (Pinusechinata) needles exposed to acid rain and ozone
Authors: Paynter Valerie A. , Reardon John C. , Shelburne Victor B.
Published: July 2007

Four genotypes of shortleaf pine (Pinusechinata Mill.) were grown in open-top chambers in the Piedmont Region of South Carolina. The seedlings were exposed to several combinations of ozone (near zero, ambient, 1.7 × ambient, or 2.5 × ambient) and acid rain (pH 3.3, 4.3, or 5.3). Glucose, sucrose, total reducing sugars, and starch contents of the pine needles were determined initially and at 5- to 12-week intervals during the following 38 weeks of exposure. Needles exposed to acid rain and ozone treatments followed the seasonal trends normally encountered in carbohydrate content, but there were some statistically significant differences in the quantities of individual carbohydrate components after prolonged exposure. In general, those needles exposed to higher levels of ozone (1.7 or 2.5 × ambient) had lower levels of starch and sucrose, with higher levels of both glucose and total reducing sugars. The starch levels in needles exposed to elevated ozone showed decreased values throughout the dormant period at all pH levels. Similarly, the sucrose levels were significantly lower in the high ozone and high acid rain treatment after 38 weeks of exposure. These results indicate that air pollutants may be affecting the carbon allocation balance within the needles.
Fire ecology of red pine (Pinusresinosa) in northern Vermont, U.S.A.
Authors: Engstrom F. Brett , Mann Daniel H.
Published: July 2007

Red pines (Pinusresinosa Ait.) in northern New England exist within small islands of fire-prone habitat surrounded by relatively nonflammable, deciduous forest. We studied the fire history and age structure of six red pine stands at an upland site in northwestern Vermont. Red pine is dominant in the canopy but rare in seedling and sapling size classes. Red pine is usually dependent on fires for regeneration. Fire scars record at least 17 different fires in the study area between the early 1800s and 1922. No fires are recorded between 1922 and 1987. The survival of numerous saplings in burned stands indicates that most of the fires were light surface fires. At least eight fires preceded periods of red pine recruitment recorded by the ages of living trees. These fires were probably locally intense, tree-killing fires. A similar regime of frequent, nonlethal fires and infrequent, lethal fires occurs in other parts of red pine's range.
The light interception index: a potential tool for assisting in vegetation management decisions
Authors: DeLong S. Craig
Published: July 2007

Light interception by vegetation canopies surrounding white spruce (Piceaglauca (Moench) Voss) was studied for four different vegetation complexes on two sites near Prince George, British Columbia. Measurements of canopy percent cover and height, and canopy proximity to the tree, were combined to provide an index that could predict light interception by the canopy. Rates of foliage development of the different vegetation canopies studied had a significant effect on their degree of light interception over the growing season. Canopies dominated by fireweed (Epilobiumangustifolium L.) developed foliage at a faster rate than canopies dominated by other species, especially those dominated by thimbleberry (Rubusparviflorus Nutt.). Understanding the light interception characteristics of different vegetation canopies along with crop tree light requirements should allow the use of the light interception index for assessing the severity of competition for light in young plantations.
Effect of growth rate and wind sway on the relation between mechanical and water-flow properties in slash pine seedlings
Authors: Dean Thomas J.
Published: July 2007

The objective of this experiment was to measure the simultaneous response of mechanical and water-flow properties in slash pine (Pinuselliottii Engelm. var. elliottii) seedlings to changes in growth rate and wind sway. Seedlings from a single half-sib family were grown in field plots and subjected to (i) whole-plot treatments of weeding, fertilization, and irrigation (complete), or no weeding, fertilization, and irrigation (control) and (ii) subplot treatments of staking or free to sway. Mechanical properties were analyzed in relation to Euler buckling and cantilever beam theory, and water-flow properties were analyzed with the interrelationship of leaf area (Al), the height to the center of leaf area (l), sapwood cross-sectional area (As), and sapwood permeability (k). Data showed that the complete treatment did not have a significant effect on either the stress required for Euler buckling or the bending stress generated by a lateral stem movement. Staking, however, significantly decreased critical buckling stress and significantly increased bending stress. Both treatments significantly reduced the ratio between All and Ask primarily through increases in k. The results suggest that k is determined more by the mechanical stresses experienced by the stem than by the water-flow properties of the stem. This linkage may allow the seedling to increase k quickly and, thus, set the stage for waterflow properties of the mature tree.
Fire regimes of western larch – lodgepole pine forests in Glacier National Park, Montana
Authors: Barrett Stephen W. , Arno Stephen F. , Key Carl H.
Published: July 2007

We conducted a detailed investigation of fire frequencies, patterns of fire spread, and the effects of fire on tree succession in the western larch – lodgepole pine (Larixoccidentalis – Pinuscontorta var. latifolia) forests west of the Continental Divide in Glacier National Park, Montana. Master fire chronologies for 1650 to the present were constructed based on tree fire scars and fire-initiated age-classes. Two kinds of primeval fire regimes were identified: (i) a mixed-severity regime ranging from nonlethal underburns to stand-replacing fires at mean intervals of 25–75 years and (ii) a regime of infrequent stand-replacing fires at mean intervals of 140–340 years. The former regime is characteristic of the North Fork Flathead valley and appears to be linked to a relatively dry climate and gentler topography compared with the McDonald Creek – Apgar Mountains and Middle Fork Flathead areas, where the latter fire regime predominates. Fire frequency in the entire North Fork study area was 20 fire years per century prior to 1935 and 2 per century after 1935. In the other two study areas it was 3–5 per century both before and after 1935. We suggest that fire suppression has altered the primeval fire regime in the North Fork, but not in the central and southern areas.
Influence of photoperiod on shoot and root frost tolerance and bud phenology of white spruce seedlings (Piceaglauca)
Authors: Bigras Francine J. , D'Aoust André L.
Published: July 2007

To determine frost tolerance of shoots and roots and the phenology of apical buds under different photoperiods during hardening and dehardening, 16-week-old white spruce seedlings (Piceaglauca (Moench) Voss) were hardened in growth chambers under 8-, 10-, 12-, and 14-h photoperiods for 14 d at 15:10 °C, followed by 14 d at each of the day:night temperatures of 12:8 °C, 10:5 °C, 5:2 °C under 13-h photoperiod, and finally, stored for 35 d at 0:0 °C in darkness. Afterwards, deacclimation conditions consisted of 14 d at 10:5 °C and 17 d at 15:10 °C with 15-h photoperiod. Frost tolerance was assessed at intervals, and phenology of apical buds was monitored by visual examination. The root dry mass remaining after removal of dead tissue was weighed 30 d after the freezing test to estimate frost damage to the root system. Results showed that hardening of shoots was influenced by photoperiod, whereas hardening of roots responded only to temperature. Frost tolerance of shoots was enhanced and bud formation accelerated under 8-h photoperiod. After 56 d of acclimation, frost tolerance of shoots reached −30, −17, −17, and −12 °C under photoperiods of 8, 10, 12, and 14 h, respectively. Bud break occurred earlier, in a similar fashion for plants treated with 8- and 10-h photoperiods. The root dry mass remaining after removal of dead tissue provided a reliable estimate of frost damage to root systems. Finally, we propose that short-day treatment accelerates and long-day treatment delays the dormancy development, thus causing all developmental processes to be affected. Consequently, hardiness development can also be accelerated by short-day treatment or delayed by long-day treatment, resulting in faster rates of hardening, dehardening, and bud break for seedlings of the short-day treatment, whereas long-day treatment delays those processes. These results complement the analysis of dehardening and bud break in the degree growth stage model described by L.H. Fuchigami and coworkers.
Somatic embryogenesis in butternut, Juglanscinerea
Authors: Pijut Paula M.
Published: July 2007

Immature cotyledonary explants excised from developing fruits of Juglanscinerea L. were cultured in vitro to induce regeneration of somatic embryos. Somatic embryos were initiated directly on cotyledons collected 9 weeks postanthesis and cultured on a Driver and Kuniyuki medium supplemented with 250 mg/L L-glutamine, 0.01 mg/L indole-3-butyric acid, 1 mg/L 6-benzylaminopurine, and 2 mg/L kinetin for 3 weeks, prior to transfer to hormone-free Driverand Kuniyuki medium. Embryogenic callus was initiated on explants collected 8–11 weeks postanthesis and cultured on two different media formulations containing 0.25 mg/L 6-benzylaminopurine and 2 mg/L 2,4-dichlorophenoxyacetic acid for 3 weeks, prior to transfer to hormone-free media. Globular to mature somatic embryos were differentiated, and conversion of somatic embryos into whole plants was incomplete. Competence of embryogenic callus was maintained for 1 year with regular subculturing on hormone-free media.