bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Basis of UropathogenicEscherichia coliEvasion of the Innate Immune Response in the Bladder
Authors: Billips Benjamin K. , Schaeffer Anthony J. , Klumpp David J.
Published: June 2008

In the urinary tract, the innate immune system detects conserved bacterial components and responds to infection by activating the proinflammatory transcription factor NF-κB, resulting in cytokine secretion and neutrophil recruitment. UropathogenicEscherichia coli(UPEC), however, has been shown to evade the host innate immune response by suppressing NF-κB activation in urothelial cells, which results in decreased cytokine secretion and increased urothelial apoptosis. To understand the molecular basis of UPEC modulation of inflammation, we performed a genetic screen with UPEC strain NU14 to identify genes which are required for modulation of urothelial cytokine secretion. Disruption ofampG(peptidoglycan permease),waaL(lipopolysaccharide O antigen ligase), oralr(alanine racemase) resulted in increased urothelial interleukin-8 (IL-8) and IL-6 release from urothelial cell cultures. Targeted deletion of these genes also resulted in elevated urothelial cytokine production during UPEC infection. Conditioned media from bacterial cultures of NU14 ΔampGand NU14 ΔwaaLcontained a heat-stable factor(s) which stimulated greater urothelial IL-8 secretion than that in NU14-conditioned medium. In a mouse model of urinary tract infection, NU14 ΔampG, NU14 ΔwaaL, and NU14 Δalrwere attenuated compared to wild-type NU14 and showed reduced fitness in competition experiments. Instillation of NU14 ΔampGor NU14 ΔwaaLincreased bladder neutrophil recruitment, indicating that enhanced urothelial cytokine secretion during urinary tract infection results in an altered host response. Thus, UPEC evasion of innate immune detection of bacterial components, such as lipopolysaccharide and peptidoglycan fragments, is likely an important factor in the ability of UPEC to colonize the urinary tract.
EspF Interacts with Nucleation-Promoting Factors To Recruit Junctional Proteins into Pedestals for Pedestal Maturation and Disruption of Paracellular Permeability
Authors: Peralta-Ramírez Janneth , Hernandez J. Manuel , Manning-Cela Rebeca , Luna-Muñoz José , Garcia-Tovar Carlos , Nougayréde Jean-Philippe , Oswald Eric , Navarro-Garcia Fernando
Published: June 2008

Many pathogenic bacteria subvert normal host cell processes by delivering effector proteins which mimic eukaryotic functions directly into target cells. EspF is a multifunctional protein injected into host cells by attaching and effacing pathogens, but its mechanism of action is not understood completely. In silico analyses of EspF revealed two key motifs: proline-rich domains and PDZ domain binding motifs. Such functional domains may allow EspF to act as an actin nucleation-promoting factor by mimicking host proteins. In agreement with these predictions, we found that EspF from rabbit enteropathogenic
Escherichia coli
(E22) participates in the regulation of actin polymerization by binding to a complex of proteins at the tight junctions (TJ). EspF bound to actin and profilin throughout the course of infection. However, after 2 h of infection, EspF also bound to the neural Wiskott-Aldrich syndrome protein and to the Arp2/3, zonula occludens-1 (ZO-1), and ZO-2 proteins. Moreover, EspF caused occludin, claudin, ZO-1, and ZO-2 redistribution and loss of transepithelial electrical resistance, suggesting that actin sequestration by EspF may cause local actin depolymerization leading to EspF-induced TJ disruption. Furthermore, EspF caused recruitment of these TJ proteins into the pedestals. An E22 strain lacking EspF did not cause TJ disruption and pedestals were smaller than those induced by the wild-type strain. Additionally, the pedestals were located mainly in the TJ. The overexpression of EspF caused bigger pedestals located along the length of the cells. Thus, actin sequestration by EspF allows the recruitment of junctional proteins into the pedestals, leading to the maturation of actin pedestals and the disruption of paracellular permeability.
A
Listeria monocytogenes
Mutant Defective in Bacteriophage Attachment Is Attenuated in Orally Inoculated Mice and Impaired in Enterocyte Intracellular Growth
Authors: Spears Patricia A. , Suyemoto M. Mitsu , Palermo Angela M. , Horton John R. , Hamrick Terri S. , Havell Edward A. , Orndorff Paul E.
Published: June 2008

A
Listeria monocytogenes
bacteriophage was used to identify a phage-resistant Tn
917
insertion mutant of the mouse-virulent listerial strain F6214-1. The mutant was attenuated when it was inoculated orally into female A/J mice and failed to replicate efficiently in cultured mouse enterocytes. Phage binding studies indicated that the mutant had a cell surface alteration that precluded phage attachment. All phenotypes associated with the mutation could be complemented in
trans
by a single open reading frame (ORF) that corresponded to the ORF interrupted by the Tn
917
insertion. The complementation effected was, in all cases, at a level indistinguishable from that of the parent. The Tn
917
insertion interrupted a gene that is predicted to encode a group 2 glycosyl transferase (provisionally designated
glcV
). A similar
glcV
gene is present in
Listeria welshimeri
and
Listeria innocua
and in some serotypes of
L. monocytogenes
. We speculate that the loss of the
glcV
product results in a defective phage receptor and that this alteration coincidentally influences a feature of the normal host-pathogen interaction required for virulence. Interestingly, the
glcV
lesion, while preventing phage attachment, did not alter the mutant's ability to bind to cultured mouse enterocyte monolayers. Rather, the mutation appeared to alter a subsequent step in intracellular replication measured by a reduction in plaque-forming efficiency and plaque size. In vivo, the mutant was undetectable in the liver and spleen 48 h after oral inoculation. The mutation is significant in part because it is one of the few that produce attenuation when the mutant is delivered orally.
Alterations of Splenic Architecture in Malaria Are Induced Independently of Toll-Like Receptors 2, 4, and 9 or MyD88 and May Affect Antibody Affinity
Authors: Cadman Emma T. , Abdallah Asmahan Y. , Voisine Cécile , Sponaas Anne-Marit , Corran Patrick , Lamb Tracey , Brown Douglas , Ndungu Francis , Langhorne Jean
Published: June 2008

Splenic microarchitecture is substantially altered during acute malaria infections, which may affect the development and regulation of immune responses. Here we investigated whether engagement of host Toll-like receptor 2 (TLR2), TLR4, TLR9, and the adaptor protein MyD88 is required for induction of the changes and whether antibody responses are modified when immunization takes place during the period of splenic disruption. The alterations in splenic microarchitecture were maximal shortly after the peak of parasitemia and were not dependent on engagement of TLR2, TLR4, or TLR9, and they were only minimally affected by the absence of the MyD88 adaptor molecule. Although germinal centers were formed in infected mice, they did not contain the usual light and dark zones. Immunization of mice with chicken gamma globulin 2 weeks prior to acutePlasmodium chabaudiinfection did not affect the quantity or avidity of the immunoglobulin G antibody response to this antigen. However, immunization at the same time as the primaryP. chabaudiinfection resulted in a clear transient reduction in antibody avidity in the month following immunization. These data suggest that the alterations in splenic structure, particularly the germinal centers, may affect the quality of an antibody response during a malaria infection and could impact the development of immunity to malaria or to other infections or immunizations given during a malaria infection.
Sex Hormone Influence on Hepatitis in Young Male A/JCr Mice Infected withHelicobacter hepaticus
Authors: Theve Elizabeth J. , Feng Yan , Taghizadeh Koli , Cormier Kathleen S. , Bell David R. , Fox James G. , Rogers Arlin B.
Published: June 2008

Hepatitis B virus (HBV), the leading cause of human hepatocellular carcinoma, is especially virulent in males infected at an early age. Likewise, the murine liver carcinogenHelicobacter hepaticusis most pathogenic in male mice infected before puberty. We used this model to investigate the influence of male sex hormone signaling on infectious hepatitis. Male A/JCr mice were infected withH. hepaticusor vehicle at 4 weeks and randomized into surgical and pharmacologic treatment groups. Interruption of androgen pathways was confirmed by hormone measurements, histopathology, and liver gene and Cyp4a protein expression. Castrated males and those receiving the competitive androgen receptor antagonist flutamide had significantly less severe hepatitis as determined by histologic activity index than intact controls at 4 months. Importantly, the powerful androgen receptor agonist dihydrotestosterone did not promote hepatitis. No effect on hepatitis was evident in males treated with the 5α-reductase inhibitor dutasteride, the peroxisome proliferator-activated receptor-α agonist bezafibrate, or the nonsteroidal anti-inflammatory drug flufenamic acid. Consistent with previous observations of hepatitis-associated liver-gender disruption, transcriptional alterations involved both feminine (cytochrome P450 4a14) and masculine (cytochrome P450 4a12 and trefoil factor 3) genes, as well gender-neutral (H19 fetal liver mRNA, lipocalin 2, and ubiquitin D) genes. Hepatitis was associated with increased unsaturated C18long-chain fatty acids (oleic acid and linoleic acid) relative to saturated stearic acid. Our results indicate that certain forms of androgen interruption can inhibitH. hepaticus-induced hepatitis in young male mice, whereas androgen receptor agonism does not worsen disease. This raises the possibility of targeted hormonal therapy in young male patients with childhood-acquired HBV.
Escherichia coliDraE Adhesin-Associated Bacterial Internalization by Epithelial Cells Is Promoted Independently by Decay-Accelerating Factor and Carcinoembryonic Antigen-Related Cell Adhesion Molecule Binding and Does Not Require the DraD Invasin
Authors: Korotkova Natalia , Yarova-Yarovaya Yuliya , Tchesnokova Veronika , Yazvenko Nina , Carl Mike A. , Stapleton Ann E. , Moseley Steve L.
Published: June 2008

The Dr family ofEscherichia coliadhesins are virulence factors associated with diarrhea and urinary tract infections. Dr fimbriae are comprised of two subunits. DraE/AfaE represents the major structural, antigenic, and adhesive subunit, which recognizes decay-accelerating factor (DAF) and carcinoembryonic antigen (CEA)-related cell adhesion molecules (CEACAMs) CEA, CEACAM1, CEACAM3, and CEACAM6 as binding receptors. The DraD/AfaD subunit caps fimbriae and has been implicated in the entry of Dr-fimbriatedE. coliinto host cells. In this study, we demonstrate that DAF or CEACAM receptors independently promote DraE-mediated internalization ofE. coliby CHO cell transfectants expressing these receptors. We also found that DraE-positive recombinant bacteria adhere to and are internalized by primary human bladder epithelial cells which express DAF and CEACAMs. DraE-mediated bacterial internalization by bladder cells was inhibited by agents which disrupt lipid rafts, microtubules, and phosphatidylinositol 3-kinase (PI3K) activity. Immunofluorescence confocal microscopic examination of epithelial cells detected considerable recruitment of caveolin, β1integrin, phosphorylated ezrin, phosphorylated PI3K, and tubulin, but not F-actin, by cell-associated bacteria. Finally, we demonstrate that the DraD subunit, previously implicated as an “invasin,” is not required for β1integrin recruitment or bacterial internalization.
Identification of
fevR
, a Novel Regulator of Virulence Gene Expression in
Francisella novicida
Authors: Brotcke Anna , Monack Denise M.
Published: June 2008

Francisella tularensis
infects wild animals and humans to cause tularemia. This pathogen targets the cytosol of macrophages, where it replicates using the genes in the
Francisella
pathogenicity island (FPI). Virulence gene regulation in
Francisella
is complex, but transcriptional regulators MglA and SspA have been shown to regulate the expression of approximately 100 genes, including the entire FPI. We utilized a
Francisella novicida
transposon mutant library to identify additional regulatory factors and identified five additional genes that are essential for virulence gene expression. One regulatory gene, FTN_0480 (
fevR
,
Francisella e
ffector of
v
irulence
r
egulation), present in all
Francisella
species, is required for expression of the FPI genes and other genes in the MglA/SspA regulon. The expression of
fevR
is positively regulated by MglA. However, constitutive expression of
fevR
in an
mglA
mutant strain did not restore expression of the MglA/SspA regulon, demonstrating that
mglA
and
fevR
act in parallel to positively regulate virulence gene expression. Virulence studies revealed that
fevR
is essential for bacterial replication in macrophages and in mice, where we additionally show that
fevR
is required for the expression of genes in the MglA/SspA regulon in vivo. Thus,
fevR
is a crucial virulence gene in
Francisella
, required for the expression of virulence factors known to be essential for this pathogen's subversion of host defenses and pathogenesis in vivo.
Characterization of
Klebsiella pneumoniae
Type 1 Fimbriae by Detection of Phase Variation during Colonization and Infection and Impact on Virulence
Authors: Struve Carsten , Bojer Martin , Krogfelt Karen Angeliki
Published: June 2008

Klebsiella pneumoniae
is recognized as an important gram-negative opportunistic pathogen. The ability of bacteria to adhere to host structures is considered essential for the development of infections; however, few studies have examined the influence of adhesion factors on
K. pneumoniae
virulence. In this study, we cloned and characterized the type 1 fimbria gene cluster of a clinical
K. pneumoniae
isolate. Although this cluster was not identical to the
Escherichia coli
type 1 fimbria gene cluster, an overall high degree of structural resemblance was demonstrated. Unique to the
K. pneumoniae fim
gene cluster is the
fimK
gene, whose product contains an EAL domain, suggesting that it has a role in regulation of fimbrial expression. Like expression of type 1 fimbriae in
E. coli
, expression of type 1 fimbriae in
K. pneumoniae
was found to be phase variable, and an invertible DNA element (
fim
switch) was characterized. An isogenic type 1 fimbria mutant was constructed and used to evaluate the influence of type 1 fimbriae in different infection models. Type 1 fimbriae did not influence the ability of
K. pneumoniae
to colonize the intestine or infect the lungs, but they were determined to be a significant virulence factor in
K. pneumoniae
urinary tract infection. By use of a PCR-based assay, the orientation of the
fim
switch during colonization and infection was investigated and was found to be all “off” in the intestine and lungs but all “on” in the urinary tract. Our results suggest that during colonization and infection, there is pronounced selective pressure in different host environments for selection of either the type 1 fimbriated or nonfimbriated phenotype of
K. pneumoniae
.
Galactose Residues on the Lipooligosaccharide ofMoraxella catarrhalis26404 Form the Epitope Recognized by the Bactericidal Antiserum from Conjugate Vaccination
Authors: Yu Shengqing , Xie Hang , Datta Anup , Naidu Natasha , Gu Xin-Xing
Published: June 2008

Lipooligosaccharide (LOS) fromMoraxella catarrhalishas the potential to elicit bactericidal antibodies against the pathogen. We generated LOS-based conjugate vaccines that elicited bactericidal antibodies in animal models. However, epitopes on the LOS recognized by the functional anti-LOS antibodies remain unidentified. In this study, a mutant strain, D4, which lost the recognition by a bactericidal anti-LOS rabbit serum in Western blotting was generated from a serotype C strain 26404 by random transposon mutagenesis. Sequence analysis revealed there was an insertion of a kanamycin resistance gene in thelgt2gene of D4, which encodes β(1-4)-galactosyltransferase. An isogeniclgt2mutant, 26404lgt2, was constructed. Structural analysis indicated that the mutant strain produced a truncated LOS lacking terminal galactoses from 4- and 6-linked oligosaccharide chains of strain 26404. Further studies showed that the antiserum lost the recognition of both mutant cells and LOSs in Western blotting, an enzyme-linked immunosorbent assay (ELISA), or a flow cytometry assay. The antiserum also lost the ability to kill the mutant strain in a bactericidal assay, whereas it showed a bactericidal titer of 1:80 to strain 26404. In an inhibition ELISA,d-(+)-galactose or 26404lgt2 LOS showed no inhibition. However, the 26404 LOS and a serotype A O35E LOS with terminal galactoses on its 6-linked oligosaccharide chain showed >90% inhibition, while a serotype B 26397 LOS showed >60% inhibition. These studies suggest that the terminal α-Gal-(1→4)-β-Gal on the 6-linked oligosaccharide chain of 26404 LOS plays a critical role in forming the epitope recognized by the bactericidal antiserum induced by immunization with our conjugate vaccine.
Caspase-1 Activation in Macrophages Infected with
Yersinia pestis
KIM Requires the Type III Secretion System Effector YopJ
Authors: Lilo Sarit , Zheng Ying , Bliska James B.
Published: June 2008

Pathogenic
Yersinia
species utilize a type III secretion system (T3SS) to translocate effectors called
Yersinia
outer proteins (Yops) into infected host cells. Previous studies demonstrated a role for effector Yops in the inhibition of caspase-1-mediated cell death and secretion of interleukin-1β (IL-1β) in naïve macrophages infected with
Yersinia enterocolitica
. Naïve murine macrophages were infected with a panel of different
Yersinia pestis
and
Yersinia pseudotuberculosis
strains to determine whether Yops of these species inhibit caspase-1 activation. Cell death was measured by release of lactate dehydrogenase (LDH), and enzyme-linked immunosorbent assay for secreted IL-1β was used to measure caspase-1 activation. Surprisingly, isolates derived from the
Y. pestis
KIM strain (e.g., KIM5) displayed an unusual ability to activate caspase-1 and kill infected macrophages compared to other
Y. pestis
and
Y. pseudotuberculosis
strains tested. Secretion of IL-1β following KIM5 infection was reduced in caspase-1-deficient macrophages compared to wild-type macrophages. However, release of LDH was not reduced in caspase-1-deficient macrophages, indicating that cell death occurred independently of caspase-1. Analysis of KIM-derived strains defective for production of functional effector or translocator Yops indicated that translocation of catalytically active YopJ into macrophages was required for caspase-1 activation and cell death. Release of LDH and secretion of IL-1β were not reduced when actin polymerization was inhibited in KIM5-infected macrophages, indicating that extracellular bacteria translocating YopJ could trigger cell death and caspase-1 activation. This study uncovered a novel role for YopJ in the activation of caspase-1 in macrophages.
Pneumolysin Released duringStreptococcus pneumoniaeAutolysis Is a Potent Activator of Intracellular Oxygen Radical Production in Neutrophils
Authors: Martner Anna , Dahlgren Claes , Paton James C. , Wold Agnes E.
Published: June 2008

Streptococcus pneumoniaeis a major cause of otitis media, pneumonia, meningitis, and septicemia in humans. The host defense against this pathogen largely depends on bacterial killing by neutrophils. A peculiar property of pneumococci is their tendency to undergo autolysis, i.e., autoinduced disruption of the bacterial cell wall mediated by activation of the enzyme LytA, under stationary growth conditions. LytA is a virulence factor, but the molecular background for this has not been fully clarified. Here we examine how bacterial compounds released upon autolysis affect the production of reactive oxygen species (ROS) in neutrophils. We found that theS. pneumoniaestrains A17 and D39 induced activation of the NADPH oxidase and the production of ROS in human neutrophils and that this activation was blocked when LytA was inactivated. The ROS-inducing bacterial substance released from autolyzed bacteria was identified as the cytoplasmic toxin pneumolysin. Further screening of clinical pneumococcal strains of various sero- and genotypes revealed that selected strains expressing toxins with reduced pneumolysin-dependent hemolytic activity had decreased abilities to induce ROS in neutrophils. Furthermore, a mutated form of purified pneumolysin lacking hemolytic and complement binding functions (PdT) did not induce any oxygen radical production. The ROS produced in response to pneumolysin formed mainly intracellularly, which may explain why this production was not detected previously. ROS released intracellularly may function as signaling molecules, modifying the function of neutrophils in bacterial defense.
Seismic design of concrete slabs for punching shear: a critical review of Canadian standard CSA A23.3-04
Authors: Gayed Ramez B. , Ghali Amin
Published: June 2008

Unbalanced moments, transferred between concrete flat plates and columns due to earthquakes, produce shear stresses that increase the vulnerability to brittle punching failure. Appropriate design and detailing of the slab–column joints are essential to prevent such failure. Because of the high flexibility of flat plate structures, lateral-force-resisting systems, e.g., bracings, frames or shear walls, are necessary to limit the interstorey drift ratio to specified values. The slab–column joints must have the strength and the ductility to undergo, without punching failure, the lateral displacement of the structure. In the 2004 version of the Canadian standard, CSA A23.3-04, clause 21.12.3 is added, specifying the punching shear design of slab–column connections subjected to earthquakes. The provisions of the clause are critically reviewed using a design example. It is shown that the new clause permits absence of shear reinforcement in cases that lack strength and when it requires shear reinforcement, it specifies excessive amount. Changes to the standard are proposed.
Proposal of a test specimen to evaluate the shear strength of vertical interfaces of running bond masonry walls
Authors: Capuzzo Neto Valentim , Corrêa Márcio R.S. , Ramalho Marcio A.
Published: June 2008

There is no normalized test to assess the shear strength of vertical interfaces of interconnected masonry walls. The approach used to evaluate this strength is normally indirect and often unreliable. The aim of this study is to propose a new test specimen to eliminate this deficiency. The main features of the proposed specimen are failure caused by shear stress on the vertical interface and a small number of units (blocks). The paper presents a numerical analysis based on the finite element method, with the purpose of showing the theoretical performance of the designed specimen, in terms of its geometry, boundary conditions, and loading scheme, and describes an experimental program using the specimen built with full- and third-scale clay blocks. The main conclusions are that the proposed specimen is easy to build and is appropriate to evaluate the shear strength of vertical interfaces of masonry walls.
Investigation strategies for the diagnosis of historic structures: on-site tests on Avio Castle, Italy, and Pišece Castle, Slovenia
Authors: Binda Luigia , Lualdi Maurizio , Saisi Antonella
Published: June 2008

This paper presents and discusses the results of investigations carried out by the authors on two castles that are considered as case histories within a project financed by the European Commission (project EVK4-2001-00091 ONSITEFORMASONRY), coordinated by C. Maierhofer of Bundesanstalt für Materialforschung und prüfung (BAM), Germany. An extensive investigation programme (including sonic, radar, flat-jack, coring, boroscopy, etc.) was planned to support the preservation and restoration actions of two ancient castles. The experience from this investigation shows the importance of the diagnosis project in selecting the most relevant strategies and tests for each specific problem.
Production prediction of conventional and global positioning system–based earthmoving systems using simulation and multiple regression analysis
Authors: Han Seungwoo , Hong Taehoon , Lee Sangyoub
Published: June 2008

Accurate estimation of construction production, which is composed of productivity and unit costs, allows construction planners and managers to have excellent control over current processes and to correctly predict the production of similar projects in the future. Due to the need for accurate production estimation, selection of the appropriate construction technology is a critical factor in the success of a project. This paper presents a methodology for developing a model capable of predicting productivity and unit costs using several procedures, such as actual data collection, input data generation using construction simulation, and multiple regression analysis. An earthmoving operation was analyzed to estimate the proposed methodology’s prediction of construction production. A global positioning system (GPS)–based earthmoving system was selected as the new construction technology to be compared with the conventional system, to evaluate the decision-making process at a jobsite. The proposed methodology is expected to provide users with a basis for selecting appropriate technology. The case study presented in this paper demonstrates how to utilize the proposed methodology and analyze its predicted results.
Evaluation of accident prediction for rural highways
Authors: Hildebrand Eric , Robichaud Karen , Ye Hong
Published: June 2008

This paper evaluates the accuracy of three commonly used models that predict accidents on two-lane, rural, arterial highways. The retrospective evaluation compared model outputs with empirical collision results for a sample of highway sections in the Province of New Brunswick. The analysis determined historical accident rates, identified key predictive variables, and compared the observed results with estimates from each safety model. All three models were found to significantly overestimate accident frequencies on the highway sections under study. The model generally employed in New Brunswick, MicroBENCOST, was found to yield the highest errors in estimated collisions. These findings suggest that the benefits from accident reduction are generally overestimated on highway improvement projects analyzed with these accident prediction models.
Evaluation of the new Canadian highway bridge design code shear provisions for concrete beams with fiber-reinforced polymer reinforcement
Authors: El-Sayed Ahmed K. , Benmokrane Brahim
Published: June 2008

The Canadian highway bridge design code (CHBDC) contains provisions for designing concrete members with fiber-reinforced polymer (FRP) reinforcement. In the second edition of the code, new shear design procedures for FRP-reinforced sections are provided. These procedures are consistent with those for steel-reinforced members in the code, in consideration of some modifications that account for the substantial differences between FRP and steel reinforcement. The shear approach adopted in the CHBDC follows the traditional approach of Vc + Vs for shear design. This paper presents an evaluation of this approach by comparing it with experimental shear strengths of available test data on beams longitudinally reinforced with FRP bars and with or without FRP stirrups. In addition, the CHBDC approach was compared with the FRP shear design provisions currently in effect in North America using the available test results. The comparison shows that the CHBDC method significantly underestimates the shear strength of FRP-reinforced concrete beams. A proposed modification to this method is presented and verified against available test results.
Vulnérabilité sismique des constructions de type béton armé au Nord du Maroc
Authors: Bezzazi Mohammed , Khamlichi Abdellatif , González José Ramón Arango
Published: June 2008

Dans ce travail, le concept de vulnérabilité sismique est utilisé afin de prédire le niveau moyen des dégâts pouvant se produire à grande échelle dans les bâtiments sous l’action d’une secousse sismique d’intensité connue. L’emploi de la notion de vulnérabilité est considéré dans le contexte de la typologie particulière des constructions en béton armé communément rencontrées au Nord du Maroc et n’ayant pas fait l’objet d’une conception parasismique assurant une protection adéquate. L’échelle de vulnérabilité est adaptée à partir de la méthode italienne dite « Gruppo Nazionale per la Difesa dai Terremoti » (GNDT), où un recalage des coefficients de pondération est effectué afin de mieux coller aux caractéristiques architecturales locales de ce type de constructions. Une corrélation est ensuite proposée entre l’indice des dégâts considéré comme l’effet principal recherché et les causes schématisées formellement à travers la notion de vulnérabilité. Les résultats d’une enquête menée sur le terrain après le fort tremblement de terre de magnitude 6,3 qui a frappé la région d’Al Hoceima au Nord du Maroc en 2004 ont montré que la méthode proposée permet d’évaluer correctement la vulnérabilité. Les courbes de fragilité relatives à cette typologie de bâtiments ont été enfin dressées.
Laboratory study on the relative performance of treated granular materials used for unpaved roads
Authors: Pierre Pascale , Bilodeau Jean-Pascal , Légère Glen , Doré Guy
Published: June 2008

Unpaved roads in Canada are subjected to high wheel loads and environmental factors that significantly affect their performance. As part of a larger research project, the objective of this laboratory study was to compare the relative performance of various stabilization and dust lifting resistance agents to an untreated granular material commonly used as a base and wear course on unpaved roads. The performance is compared using California bearing ratio (CBR), resilient modulus, and unconfined compression strength tests. In addition, the surface sealing potential was measured on each specimen. The effects of compaction water content, product concentration, and the environment were investigated in this study. The results show that these variables have a significant impact on the performance measured, and it was possible to identify peak performance concentrations and performing products for the conditions tested.
Design elastic input energy spectra based on Iranian earthquakes
Authors: Ghodrati Amiri Gholamreza , Darzi Gholamreza Abdollahzadeh , Vaseghi Amiri Javad
Published: June 2008

The goal of this paper is to propose input energy spectra applicable to seismic design of structures based on Iranian earthquakes. In terms of input energy, these spectra represent the load effects of a strong earthquake that a structure may encounter during its lifetime. For this purpose, from among 1800 existing earthquake records in Iran, 110 records were selected. By using these records and through dynamic response analyses, the design input energy spectra for four ground types, defined by the Iranian earthquake code of practice, have been derived.
Représentation mathématique des noeuds dans le tronc des arbres
Authors: Samson Marcel , Bindzi Isaac , Kamoso L.M.
Published: June 2008

This study is aimed at developing equations describing the shape of any particular knot in the trunk of a tree. The present model differs from previous models in that it is not limited by the assumption of a straight conical knot. The knot is represented by an assemblage of elliptical cone sections with the axis defined by a Hermite-type cubic equation or a straight line, and ends in a half ellipsoid symbolizing the enclosure of an intergrown knot. Simulations of knot shapes are presented to demonstrate the versatility of the model. The model seems flexible enough to adjust to common knot shapes presented in the literature. This model is intended to be incorporated into tree felling, bucking, and sawing simulation softwares.
How fire scars are formed: coupling a disturbance process to its ecological effect
Authors: Gutsell S.L. , Johnson E.A.
Published: June 2008

Using results from the field and laboratory, we give a detailed explanation of an important and commonly observed ecological phenomenon, fire scarring of trees. Four key observations associated with the formation of fires scars are explained using fluid dynamics and heat transfer processes. When a fire passes by a tree, its height increases on the tree's leeward side because of the occurrence of two leeward vortices. The flame height increases in the vortices because the turbulent mixing of fuel and air is suppressed. The flow of gaseous fuel in the vortices becomes greater than the rate of mixing with the air, and hence there is an increased height along which combustion can occur. Fire scars are found only on the leeward side of trees because the vortices increase the residence time of the flame on the leeward side of the tree compared with the residence time of the flame on the tree's windward side. This leads to differential heating around the tree bole. Small trees rarely have fire scars because their cambium is usually completely killed by a passing fire and (or) their foliage is killed by crown scorch. Fire scars are usually triangular in shape; wider at the base and decreasing in width with height. The triangular shape is a result of the temperature isotherms within the standing leeward flame, which are triangular in shape.
Variation of water relations parameters with extended rehydration time, leaf form, season, and proportion of leaf
Authors: Zobel Donald B.
Published: June 2008

Pressure–volume curves were measured in October, February, and July for twigs of three deciduous, three evergreen broadleaf, four pine, and two other conifer species in the southern Appalachian Mountains, U.S.A. Data were analyzed to determine the influence on water relations parameters of rehydration time, sample leafiness, leaf form, season, and species within leaf form. Results of samples rehydrated overnight did not differ significantly from results of samples rehydrated overnight plus 24 h. Leafiness (leaf dry mass/sample dry mass) was occasionally related to water relations parameters. Water relations parameters usually varied with leaf form, and occasionally with sampling location. Patterns of variation among leaf forms differed for each combination of parameter and season: the strongest generality was that leafy deciduous twigs and pines had high tissue elasticity, whereas evergreen broadleaf species had low elasticity. Evergreen broadleaf species had a consistently high relative water content at zero turgor. Compared with literature values, these species had average to very high osmotic potentials. There was little consistency of water relations parameters among leaf forms and seasons in the overall (literature and current) data, although osmotic potential of all evergreen leaf forms rose from winter to summer.
Stem incorporation of gibberellins to promote sexual development of white spruce, Norway spruce, and jack pine
Authors: Fogal W.H. , Jobin G. , Schooley H.O. , Coleman S.J. , Wolynetz M.S.
Published: June 2008

Stem incorporation of gibberellins (GA4/7 60:40) by injecting a liquid formulation or implanting a solid formulation was evaluated for promoting sexual reproductive development and for effects on vegetative development and foliage chlorosis in seedling and grafted white spruce, Piceaglauca (Moench) Voss; seedling Norway spruce, Piceaabies (L.) Karst.; and jack pine, Pinusbanksiana Lamb., seed trees. Spruces were treated with a single application of 0.76 or 1.53 mg GA4/7 per square centimetre of stem cross-sectional area at breast height during the late stage of shoot elongation (June 9 for white spruce and June 19 and 20 for Norway spruce). Jack pine was treated with a single early (July 5) or late (August 15) application of 1.53 mg GA4/7/cm2 or a split early–late application of 0.76 mg GA4/7/cm2. Results were evaluated in the subsequent season (i) by counting seed and pollen strobili, developing vegetative shoots, latent vegetative buds, and dead buds and (ii) by assessing foliage chlorosis and mortality. The numbers of seed strobili were increased by injections of GA4/7 at low and high application rates on seedling white spruce and Norway spruce and by the high application rate on grafted white spruce; implants were effective on seedling white and Norway spruce at the high application rate. In jack pine, the number of seed strobili was not increased by GA4/7. The numbers of pollen strobili were not significantly increased by GA4/7 treatments to white spruce or Norway spruce but were increased on jack pine by a single early injection at the high rate and split injections at the low rate. The number of developing vegetative shoots was reduced by GA4/7 injections at both rates on white spruce grafted trees and Norway spruce; the implants reduced them only on the grafted white spruce given the low rate. For the spruces, treatments with GA4/7 did not influence bud mortality. Foliage chlorosis and mortality, evident on jack pine but not on white or Norway spruce trees, was more severe with injections than with implants.
Ecosystem nutrient responses to chronic nitrogen inputs at Fernow Experimental Forest, West Virginia
Authors: Gilliam Frank S. , Yurish Bradley M. , Adams Mary Beth
Published: June 2008

Among the current environmental concerns for forests of the eastern United States is nitrogen (N) saturation, a result of excessive inputs of N associated with acidic deposition. We studied nutrient responses on N-treated and untreated watersheds of the Fernow Experimental Forest, West Virginia, to test for evidence of N saturation on the treated watershed. The watersheds were WS7 (23-year-old even-aged control), WS4 (mature mixed-aged control), and WS3 (23-year-old even-aged treatment). WS3 has received aerial applications of (NH4)2SO4 from 1989 to the present (a total of 4 years for the study period) at 3 × ambient inputs of N and S (54 and 61 kg•ha−1•year−1, respectively). Base-flow stream samples were collected weekly from each watershed and analyzed for NO3− and Ca2+. Mineral soil was incubated in situ, placed in bags, and buried about every 30 days during the growing season in each of seven sample plots within each watershed. Moist samples of soil from the bags were analyzed for extractable NH4+ and NO3−. In addition, forest floor material and leaves of an herbaceous species (Violarotundifolia Michx.) from each plot were analyzed for N and other nutrients. Violarotundifolia was present on all 21 plots and used as an additional indicator of N availability and soil fertility. Foliage tissue was sampled from overstory tree species (Liriodendrontulipifera L., Prunusserotina Ehrh., Betulalenta L., and Acerrubrum L.) from WS3 and WS7 and analyzed for nutrient content. Results from the 1993 growing season showed few, if any, differences among watersheds for (1) N content and C/N ratio of the mineral soil and forest floor and (2) relative proportion of NH4+ and NO3− produced in the buried bags. Nitrification rates were equally high in soils of all watersheds; N concentrations were significantly higher in foliage tissue of overstory tree species and of V. rotundifolia in the treatment versus control watersheds; plant tissue Ca was significantly lower for the treatment watershed than for the control watersheds. Our results support the conclusions of earlier studies that high amounts of ambient N deposition have brought about N saturation on untreated watersheds at the Fernow Experimental Forest. This is suggested by minimal differences among watersheds in N mineralization and nitrification and soil and forest floor N. However, aggravated N saturation on our treated watershed can be seen in differences in plant tissue nutrients among watersheds and streamflow data, indicating increased losses of NO3− with accompanying losses of Ca2+ in response to further N additions to a N-saturated system.
Forest cover types derived from Landsat Thematic Mapper imagery for Changbai Mountain area of China
Authors: Shao Guofan , Shugart Herman H. , Zhao Guang , Zhao Shidong , Wang Shaoxian , Schaller Jörg
Published: June 2008

The distributions of various forest cover types on Changbai Mountain of northeastern China were examined by interpreting Landsat Thematic Mapper satellite data. The area studied consists of the Changbai Nature Reserve plus an 8 km wide buffer zone. The dominant forest cover types were mixed Korean pine (Pinuskoraiensis Sieb. & Zucc.) hardwood forest below 1100 m above sea level (asl) and evergreen coniferous forest between 1100 and 1650 m asl. These two forest cover types accounted for about 70% of the area inside the reserve, and 50% of the area outside the reserve. Other forest cover types included aspen (Populusdavidiana Dode) –white birch (Betulaplatyphylla Sukachev) forest, hardwood forest, larch (Larixolgensis A. Henry) forest, sparse forest land, and mountain birch (Betulaermanii Cham.) forest. Above the forest line (1950 m asl), a zone of tundra was distributed on the top of Changbai Mountain. The mountain birch forest was located between tundra and the evergreen forest. Human-altered areas, including forest clearcuts and urban areas, accounted for only 10% of the whole study area. More than 90% (in area) of the human-altered areas was found in the zone surrounding the reserve. To better protect the old-growth forest ecosystems inside and outside Changbai Nature Reserve, conservation planning for the reserve and forest management for the surrounding area need to be modified.
Vegetation–site relationships of witness trees (1780–1856) in the presettlement forests of eastern West Virginia
Authors: Abrams Marc D. , McCay Deanna M.
Published: June 2008

Witness tree data from 1780–1856 for the Monongahela National Forest in eastern West Virginia were analyzed with respect to physiographic unit (Ridge and Valley versus Allegheny Mountains) and landform, and compared with present-day forest composition. Contingency table analysis and standardized residuals were used to quantify the preference or avoidance of common tree species with various landforms. Pre-European settlement forests in the Ridge and Valley were dominated by mixed oak (Quercusalba L., Quercusprinus L., Quercusvelutina Lam. and Quercusrubra L.), Pinus spp., Castaneadentata (Marsh.) Borkh., and Carya on ridge sites and Q. alba, Acersaccharum Marsh., Pinus, Tiliaamericana L., and Tsugacanadensis (L.) Carr. on valley floors. The original forests in the Allegheny Mountains were dominated by Fagusgrandifolia Ehrh., T. canadensis, A. saccharum, Acerrubrum L., Betula spp., and Pinus, with predominantly Fagus–Tsuga–Pinus forests on mountain tops and Tsuga–Acer–Betula forests on valley floors. Compared with the presettlement era, present-day forests on both physiographic units lack overstory C. dentata and have decreased Pinus and (or) Q. alba. Species that have increased substantially following Euro-American settlement include Q. prinus, Q. rubra, Quercuscoccinea Muenchh., and A. rubrum in the Ridge and Valley and Prunusserotina Ehrh., A. rubrum, and Betula spp. in the Allegheny Mountains. These dramatic changes in forest composition were attributed to the chestnut blight (caused by Endothiaparasitica (Murrill) P.J. Anderson & H.W. Anderson), widespread logging, intensive wildfires, and more recently, fire exclusion.
Soil compaction and conifer growth after tractor yarding at three coastal Washington locations
Authors: Miller Richard E. , Scott William , Hazard John W.
Published: June 2008

We measured soil density and tree growth after wet-season, ground-based yarding on fine-textured soils at three clear-cut sites. Four treatment conditions were sampled on or near four skid trails (replicates): nontilled and tilled primary skid trails, and adjacent slash-treated areas; the fourth treatment was secondary skid trails at two locations and a logged-only control at the third location. The 16 treatment plots were split into 4 subplots, each randomly assigned to a species–stock type and planted with 30 seedlings. Tree data through year 8 after planting were analyzed as a randomized block, split-plot design. Compared with nontrail areas, bulk density in the 0- to 8-cm depth on primary skid trails after logging averaged 41–52% greater. Eight years later, bulk density in the 0- to 30-cm depth of primary skid trails still exceeded that outside trails by about 20%, yet tree survival was similar except for western hemlock (Tsugaheterophylla (Raf.) Sarg.) having poorer survival on nontilled trails at one location. Average tree height and volume of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco var. menziesii), Sitka spruce (Piceasitchensis (Bong.) Carr.), and hemlock (except height at one location) did not differ among treatments. Observed differences among treatment means were small. Power analyses indicated that 20% or larger differences in tree height or volume were detectable with 30–95% power.
Estimating large-root biomass from stump and breast-height diameters for Douglas-fir in western Oregon
Authors: Thies Walter G. , Cunningham Patrick G.
Published: June 2008

Estimates of belowground biomass are fundamental to understanding carbon cycling and sequestration and the dynamics of ecological systems and in designing studies of those systems. An important belowground component of stands in the Pacific Northwest is the large-root biomass associated with mature, second-growth, Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco). Sample Douglas-fir from four western Oregon stands were felled, and their stumps and root systems were excavated and cleaned. Biomass of all roots larger than 10 mm in diameter plus the belowground portion of the stump was determined on a dry-weight basis. Each tree was measured for stump diameter, 15 cm above the soil line, and for diameter at breast height. Regression models were constructed by using data from 82 trees from four stands. Stump diameters ranged from 24.1 to 92.5 cm, diameter at breast height ranged from 21.3 to 54.6 cm, and biomass ranged from 20.5 to 614.4 kg.
Genetic variation in sand pine (Pinusclausa)
Authors: Parker Kathleen C. , Hamrick J.L.
Published: June 2008

Pinusclausa (Chapm. ex Engelm.) Vasey ex Sarg. is a member of subsection Contortae that is restricted to Florida and the southern tip of Alabama. The present distribution of P. clausa is divided into two purported varieties: var. clausa in peninsular Florida and var. immuginata primarily in the Florida panhandle. We determined allozyme diversity and population genetic structure for 12 populations of var. clausa and 9 populations of var. immuginata. At the species level, 88% of the 26 loci examined were polymorphic. The genetic diversity maintained at both the species (Hes = 0.100) and population (Hep = 0.092) levels was low relative to most other pine species. Genetic differentiation among populations was also relatively low (GST = 0.054). Genetic distances between populations of the same variety (mean D = 0.006) were lower than genetic distances between populations of different varieties (mean D = 0.012). Although allele frequencies at individual loci differed significantly between the two varieties, each variety maintained nearly 99% of the genetic variation apparent at the species level (intervarietal differentiation, Gv = 0.014). The lower levels of genetic diversity in P. clausa may have resulted in part from genetic bottlenecks during periods of range retraction.