bluuebunny/crossref_metadata_2025 huggingface dataset:
Electromagnetic field of a linear antenna
Authors: Derby Norman , Olbert Stanislaw
Published: October 2008

Animated computer simulations of the electric field of a radiating antenna can capture the attention of students in introductory electromagnetism courses and stimulate active discussions. The simulations raise questions not usually addressed in textbooks. In certain cases, some of the field lines appear to move toward the antenna, the speed of the field lines can change as they move, and the field lines exhibit strange behavior (circling or splitting) at certain points. Because their fields can be expressed in terms of elementary functions, animations of point dipole antennas are common, but animations showing the fields of antennas with more realistic lengths are not as common because analytical expressions for these fields are not as well known. We show that it is possible to derive analytical expressions in terms of elementary functions for the electromagnetic field of linear antennas of finite length. We draw attention to an open-source method for displaying the fine details within the field patterns and then give a general discussion of singular points and their motions, derive expressions for their location and phase velocity, and apply these results to some of the phenomena that are visible in visualizations of the fields of various antennas.
Some insights from total collapse in the N-body problem
Authors: Volchan Sérgio B.
Published: October 2008

We discuss the Sundman–Weierstrass theorem of total collapse in its historical context. This remarkable and relatively simple result, a type of stability criterion, is at the crossroads of some interesting developments in the gravitational N-body problem. We use it as motivation to explore the connections to such important concepts as integrability, singularities, and typicality in order to gain insight into the transition from a predominantly quantitative to a novel qualitative approach to dynamical problems that took place at the end of the 19th century.
A periodic structure for electronic signals and demonstration of electronic lasing
Authors: Doiron Serge , Giller Christophe , Beaudoin Normand , Haché Alain
Published: October 2008

A sequence of electronic phase shifters and partial reflectors/transmitters is shown to form a true periodic scattering structure for electronic signals, complete with stop bands, interference, and dispersion effects. An experimental demonstration at 1kHz is made with supporting theoretical results. As with conventional periodic media, sharp defect modes in the forbidden band arise when the periodicity is broken. When gain is added to the structure, a type of lasing action is observed that in almost every aspect is similar to conventional lasers.
Entropy and evolution
Authors: Styer Daniel F.
Published: October 2008

Quantitative estimates of the entropy involved in biological evolution demonstrate that there is no conflict between evolution and the second law of thermodynamics. The calculations are elementary and could be used to enliven the thermodynamics portion of a high school or introductory college physics course.
KPC-2-Producing
Enterobacter cloacae
and
Pseudomonas putida
Coinfection in a Liver Transplant Recipient
Authors: Bennett Jason W. , Herrera Monica L. , Lewis James S. , Wickes Brian W. , Jorgensen James H.
Published: October 2008

Carbapenemases are among the newest resistance mechanisms to emerge in some gram-negative bacteria. We describe bacteremia in a critically ill liver transplant recipient infected with KPC-2-producing
Enterobacter cloacae
and
Pseudomonas putida
. Although this enzyme has been previously described in
Enterobacter
spp., this is the first report of KPC carbapenemase in
P. putida
.
Polymorphism in the Human Major Histocompatibility Complex and Early Viral Decline during Treatment of Chronic Hepatitis C
Authors: Yee Leland J. , Im KyungAh , Wahed Abdus S. , Bugawan Teodorica , Li Jia , Rhodes Shannon L. , Erlich Henry , Rosen Hugo R. , Liang T. Jake , Yang Huiying
Published: October 2008

The dynamics of the viral decline immediately after the start of therapy for chronic hepatitis C virus (HCV) infection may have prognostic potential for ultimate sustained virologic response. Considerable interindividual variability in the decline has been reported, including differences by race. The human major histocompatability complex (MHC) genes encode the human leukocyte antigens, which are important in the immune response to viral infections. We examined whether carriage of specific human MHC alleles are associated with the rate of the early viral decline. Longitudinal viral level data (baseline and days 1, 2, 7, 14, and 28 of treatment), medium resolution MHC genotyping, and random coefficients models were used to examine associations between MHC class I and class II allele carriage and the dynamics of the viral decline in 180 African-Americans (AAs) and 194 Caucasian Americans (CAs) with genotype-1 HCV infection over the first 28 days of treatment with peginterferon α2a plus ribavirin. Baseline viral levels were similar by race, irrespective of allele carriage. However, the rate of change in the viral decline was associated with both allele and race. Among the four subgroups defined by race and specific allele, the fastest rates of decline were observed (in terms of estimated mean viral declines log
10
IU/ml during the first four weeks) in CA noncarriers for A*03 (2.75;
P
= 0.018), in CA carriers for Cw*03 (2.99;
P
= 0.046), and in CA noncarriers for DQA1*04 (2.66;
P
= 0.018) or DQB1*0402 (2.65;
P
= 0.018). MHC alleles are associated with the viral decline during the first 28 days of peginterferon therapy.
Efficacy of Ciprofloxacin and Moxifloxacin against
Nocardia brasiliensis
In Vitro and in an Experimental Model of Actinomycetoma in BALB/c Mice
Authors: Chacon-Moreno Brenda Edith , Welsh Oliverio , Cavazos-Rocha Norma , de la Luz Salazar-Cavazos Maria , Garza-Lozano Hector Gerardo , Said-Fernandez Salvador , Ocampo-Candiani Jorge , Vera-Cabrera Lucio
Published: October 2008

The efficacy of ciprofloxacin and moxifloxacin against
Nocardia brasiliensis
was evaluated by applying 25 mg of each drug/kg subcutaneously every 8 h in BALB/c mice infected with
N. brasiliensis
. A statistically significant difference was observed only with moxifloxacin. A moxifloxacin-trimethoprim-sulfamethoxazole combination was as active as when each compound was used alone.
Testing of Experimental Compounds in a Relapse Model of Tuberculosis Using Granulocyte-Macrophage Colony-Stimulating Factor Gene-Disrupted Mice
Authors: Woolhiser Lisa K. , Hoff Donald R. , Marietta Karen S. , Orme Ian M. , Lenaerts Anne J.
Published: October 2008

This study describes an in vivo model for evaluating the sterilizing activity of compounds against persisting
Mycobacterium tuberculosis
. The initial treatment with isoniazid and rifampin in granulocyte-macrophage colony-stimulating factor gene-disrupted mice reduced the number of bacteria more than 99% within 3 weeks. A subsequent treatment with individual drugs was performed to assess their activity on the 1% of remaining bacilli and disease relapse.
Animal Models ofStreptococcus pneumoniaeDisease
Authors: Chiavolini Damiana , Pozzi Gianni , Ricci Susanna
Published: October 2008

Streptococcus pneumoniae is a colonizer of human nasopharynx, but it is also an important pathogen responsible for high morbidity, high mortality, numerous disabilities, and high health costs throughout the world. Major diseases caused by S. pneumoniae are otitis media, pneumonia, sepsis, and meningitis. Despite the availability of antibiotics and vaccines, pneumococcal infections still have high mortality rates, especially in risk groups. For this reason, there is an exceptionally extensive research effort worldwide to better understand the diseases caused by the pneumococcus, with the aim of developing improved therapeutics and vaccines. Animal experimentation is an essential tool to study the pathogenesis of infectious diseases and test novel drugs and vaccines. This article reviews both historical and innovative laboratory pneumococcal animal models that have vastly added to knowledge of (i) mechanisms of infection, pathogenesis, and immunity; (ii) efficacies of antimicrobials; and (iii) screening of vaccine candidates. A comprehensive description of the techniques applied to induce disease is provided, the advantages and limitations of mouse, rat, and rabbit models used to mimic pneumonia, sepsis, and meningitis are discussed, and a section on otitis media models is also included. The choice of appropriate animal models for in vivo studies is a key element for improved understanding of pneumococcal disease.
Candida parapsilosis, an Emerging Fungal Pathogen
Authors: Trofa David , Gácser Attila , Nosanchuk Joshua D.
Published: October 2008

Candida parapsilosis is an emerging major human pathogen that has dramatically increased in significance and prevalence over the past 2 decades, such that C. parapsilosis is now one of the leading causes of invasive candidal disease. Individuals at the highest risk for severe infection include neonates and patients in intensive care units. C. parapsilosis infections are especially associated with hyperalimentation solutions, prosthetic devices, and indwelling catheters, as well as the nosocomial spread of disease through the hands of health care workers. Factors involved in disease pathogenesis include the secretion of hydrolytic enzymes, adhesion to prosthetics, and biofilm formation. New molecular genetic tools are providing additional and much-needed information regarding C. parapsilosis virulence. The emerging information will provide a deeper understanding of C. parapsilosis pathogenesis and facilitate the development of new therapeutic approaches for treating C. parapsilosis infections.
Human Genetic Factors and Respiratory Syncytial Virus Disease Severity
Authors: Miyairi Isao , DeVincenzo John P.
Published: October 2008

To explain the wide spectrum of disease severity caused by respiratory syncytial virus (RSV) and because of the limitations of animal models to fully parallel human RSV disease, study of genetic influences on human RSV disease severity has begun. Candidate gene approaches have demonstrated associations of severe RSV in healthy infants with genetic polymorphisms that may alter the innate ability of humans to control RSV (surfactants, Toll-like receptor 4, cell surface adhesion molecules, and others) and those that may control differences in proinflammatory responses or enhanced immunopathology (specific cytokines and their receptors). These studies are reviewed. They are valuable since an understanding of the direction of a polymorphism's effect can help construct a meaningful human RSV disease pathogenesis model. However, the direction, degree, and significance of the statistical association for any given gene are equivocal among studies, and the functional significance of specific polymorphisms is often not even known. Polymorphism frequency distribution differences associated with RSV infection arising from diversity in the genetic background of the population may be confounded further by multiple-hypothesis testing and publication bias, as well as the investigator's perceived importance of a particular pathogenic disease process. Such problems highlight the limitation of the candidate gene approach and the need for an unbiased large-scale genome-wide association study to evaluate this important disease.
Emergence and Disappearance of a Virulent Clone of
Haemophilus influenzae
Biogroup aegyptius, Cause of Brazilian Purpuric Fever
Authors: Harrison Lee H. , Simonsen Vera , Waldman Eliseu A.
Published: October 2008

In 1984, children presented to the emergency department of a hospital in the small town of Promissão, São Paulo State, Brazil, with an acute febrile illness that rapidly progressed to death. Local clinicians and public health officials recognized that these children had an unusual illness, which led to outbreak investigations conducted by Brazilian health officials in collaboration with the U.S. Centers for Disease Control and Prevention. The studies that followed are an excellent example of the coordinated and parallel studies that are used to investigate outbreaks of a new disease, which became known as Brazilian purpuric fever (BPF). In the first outbreak investigation, a case-control study confirmed an association between BPF and antecedent conjunctivitis but the etiology of the disease could not be determined. In a subsequent outbreak, children with BPF were found to have bacteremia caused by Haemophilus influenzae biogroup aegyptius (H. aegyptius), an organism previously known mainly to cause self-limited purulent conjunctivitis. Molecular characterization of blood and other isolates demonstrated the clonal nature of the H. aegyptius strains that caused BPF, which were genetically distant from the diverse strains that cause only conjunctivitis. This led to an intense effort to identify the factors causing the unusual invasiveness of the BPF clone, which has yet to definitively identify the virulence factor or factors involved. After a series of outbreaks and sporadic cases through 1993, no additional cases of BPF have been reported.
Current World Status of
Balantidium coli
Authors: Schuster Frederick L. , Ramirez-Avila Lynn
Published: October 2008

Balantidium coli is a cosmopolitan parasitic-opportunistic pathogen that can be found throughout the world. Pigs are its reservoir hosts, and humans become infected through direct or indirect contact with pigs. In rural areas and in some developing countries where pig and human fecal matter contaminates the water supply, there is a greater likelihood that balantidiosis may develop in humans. The infection may be subclinical in humans, as it mostly is in pigs, or may develop as a fulminant infection with bloody and mucus-containing diarrhea; this can lead to perforation of the colon. The disease responds to treatment with tetracycline or metronidazole. Balantidiosis is a disease that need never exist given access to clean water and a public health infrastructure that monitors the water supply and tracks infections. Its spread can be limited by sanitary measures and personal hygiene, but it is a disease that will be around as long as there are pigs. Immunocompromised individuals have developed balantidiosis without any direct contact with pigs, perhaps with rats or contaminated produce as a possible source of infection. For the clinician, balanatidiosis should be included in the differential diagnosis for persistent diarrhea in travelers to or from Southeast Asia, the Western Pacific islands, rural South America, or communities where close contact with domestic swine occurs. Warming of the earth's surface may provide a more favorable environment, even in the now-temperate areas of the world, for survival of trophic and cystic stages of Balantidium, and its prevalence may increase. Effective sanitation and uncontaminated water are the most useful weapons against infection. Fortunately, balantidiosis responds to antimicrobial therapy, and there have been no reports of resistance to the drugs of choice.
New Insights on Classification, Identification, and Clinical Relevance ofBlastocystisspp
Authors: Tan Kevin S. W.
Published: October 2008

Blastocystisis an unusual enteric protozoan parasite of humans and many animals. It has a worldwide distribution and is often the most commonly isolated organism in parasitological surveys. The parasite has been described since the early 1900s, but only in the last decade or so have there been significant advances in our understanding ofBlastocystisbiology. However, the pleomorphic nature of the parasite and the lack of standardization in techniques have led to confusion and, in some cases, misinterpretation of data. This has hindered laboratory diagnosis and efforts to understand its mode of reproduction, life cycle, prevalence, and pathogenesis. Accumulating epidemiological, in vivo, and in vitro data strongly suggest thatBlastocystisis a pathogen. Many genotypes exist in nature, and recent observations indicate that humans are, in reality, hosts to numerous zoonotic genotypes. Such genetic diversity has led to a suggestion that previously conflicting observations on the pathogenesis ofBlastocystisare due to pathogenic and nonpathogenic genotypes. Recent epidemiological, animal infection, and in vitro host-Blastocystisinteraction studies suggest that this may indeed be the case. This review focuses on such recent advances and also provides updates on laboratory and clinical aspects ofBlastocystisspp.
MgrA Represses Biofilm Formation in
Staphylococcus aureus
Authors: Trotonda María Pilar , Tamber Sandeep , Memmi Guido , Cheung Ambrose L.
Published: October 2008

MgrA is a pleiotropic regulator that controls autolysis, virulence, and efflux pump activity in
Staphylococcus aureus
. We recently found that
mgrA
mutants of strains RN6390, SH1000, and MW2 also displayed enhanced biofilm formation compared with their respective parents. The biofilms formed by
mgrA
mutants of RN6390 and MW2 are independent of
sigB
and
ica
loci, two genetic elements that have been previously associated with biofilm formation in
S. aureus
. Biofilms formed by
mgrA
mutants are dependent on the expression of surface proteins mediated by the sortase gene
srtA
. Extracellular DNA was also a crucial component of the early biofilm of
mgrA
mutants. Genetic analysis indicated that biofilm formation in
mgrA
mutants is mediated in part by
agr
RNAIII, a genetic locus regulated by
mgrA
. Additionally, SarA is important to biofilm formation in
mgrA
mutants since the double
sarA mgrA
mutants failed to form biofilms compared to single
mgrA
mutants of RN6390 and MW2. However, the SarA-mediated effect is independent of
agr
and proteases such as V8 protease and aureolysin. Collectively, our data showed MgrA to be a repressor of biofilm formation, and biofilms formed by
mgrA
mutants have features that are distinct from other reported biofilm types in
S. aureus
.
Vaccine-Induced Cellular Immune Responses Differ from Innate Responses in Susceptible and Resistant Strains of Mice Infected withCoccidioides posadasii
Authors: Shubitz Lisa F. , Dial Sharon M. , Perrill Robert , Casement Rachael , Galgiani John N.
Published: October 2008

Susceptibility toCoccidioidesspp. varies widely in humans and other mammals and also among individuals within a species. Among strains of mice with various susceptibilities, immunohistopathology revealed that C57BL/6 mice were highly susceptible to the disease following intranasal infection, DBA/2n mice were intermediate, and Swiss-Webster mice were innately resistant. Resistant Swiss-Webster mice developed prominent perivascular/peribronchiolar lymphocytic cuffing and well-formed granulomas with few fungal elements and debris in the necrotic center, surrounded by a mantle of macrophages, lymphocytes, and fibrocytes. Susceptible C57BL/6 mice became moribund between 14 and 18 days postinfection, with overwhelming numbers of neutrophils and spherules and very few T cells, the drastic reduction of which was associated with failure and death, while intermediate DBA/2n mice controlled the fungal burden but demonstrated progressive lung inflammation with prominent suppuration, and they deteriorated clinically. Vaccinated C57BL/6 mice had an early and robust lymphocyte response, which included significantly higher Mac2+, CD3+, and CD4+cell scores on day 18 than those of innately resistant SW mice and DBA/2n mice; they also had prominent perivascular/peribronchiolar lymphocytic infiltrates not present in their unvaccinated counterparts, and they appeared to be resolving lesions by day 56 compared to the other two strains, based on significantly lower disease scores and observably smaller and fewer lesions with few spherules and neutrophils.
Purification and characterization of a psychrophilic catalase from AntarcticBacillus
Authors: Wang Wei , Sun Mi , Liu Wanshun , Zhang Bin
Published: October 2008

Catalase from Bacillus sp. N2a (BNC) isolated from Antarctic seawater was purified to homogeneity. BNC has a molecular mass of about 230 kDa and is composed of four identical subunits of 56 kDa. The catalase showed optimal activity at 25 °C and at a pH range of 6–11. The enzyme could be inhibited by azide, hydroxylamine, and mercaptoethanol. These characteristics suggested that BNC is a small-subunit monofunctional catalase. The activation energy of BNC was 13 kJ/mol and the apparent kcat/Kmvalues were 3.6 × 106and 4 × 106L·mol–1·s–1at 4 and 25 °C, respectively. High catalytic efficiency of BNC at low temperatures enables this bacterium to scavenge H2O2efficiently. BNC exhibited activation energy, catalytic efficiency, and thermostability comparable with some mesophilic homologues. Such similarity of enzymatic characteristics to mesophilic homologues, although uncommon among the cold-adapted enzymes in general, has also been observed in other psychrophilic small-subunit monofunctional catalases.
Identification of genes differentially expressed in a strain of the moldAspergillus nidulanscarrying a loss-of-function mutation in thepalAgene
Authors: Silva Emiliana M. , Freitas Janaína S. , Gras Diana E. , Squina Fábio M. , Leal Juliana , Silveira Henrique C.S. , Martinez-Rossi Nilce M. , Rossi Antonio
Published: October 2008

To identify genes differentially expressed in a strain of the mold Aspergillus nidulans carrying a loss-of-function mutation in palA, a gene in the pH-responsive signal transduction pathway, suppression subtractive hybridization was performed between RNA isolated from the biA1 and biA1 palA1 strains grown under limiting inorganic phosphate at pH 5.0. We have identified several genes upregulated in the biA1 palA1 mutant strain that play important roles in mitotic fidelity, stress responses, enzyme secretion, signal transduction mechanisms, development, genome stability, phosphate sensing, and transcriptional regulation among others. The upregulation of eight of these transcripts was also validated by Northern blot. Moreover, we show that a loss of function mutation in the palA gene drastically reduced the neutral sugar content of the acid phosphatase PacA secreted by the fungus A. nidulans grown at pH 5.0 compared with a control strain.
Transposon Tn5281 is the main distributor of the aminoglycoside modifying enzyme gene among isolates of Enterococcus faecalis in Tehran hospitals
Authors: Feizabadi Mohammad Mehdi , Shokrzadeh Leila , Sayady Sara , Asadi Soroor
Published: October 2008

Infections with high levels of gentamicin-resistant (HLGR) isolates of Enterococcus faecalis are common in Tehran hospitals. Genes encoding such resistance are transmissible by conjugation at high frequency. The purpose of this study was to determine the existence of Tn5281 and its flanking aminoglycoside modifying enzyme gene aac(6′)-aph(2″) among 102 HLGR isolates of E. faecalis cultured from patients at three hospitals in Tehran, Iran. These isolates were detected by disks containing 120 μg of gentamicin and made 65% of all E. faecalis during the study period. DNA was extracted from HLGR isolates and subjected to PCR assays targeting aac(6′)-aph(2″) and conjugative transposon Tn5281. The amplified aac(6′)-aph(2″) gene was labeled with digoxigenin and probed with Tn5281 amplicons in dot blot hybridization assays. The aac(6′)-aph(2″) gene was detected in 91%–92% (n = 93) of the HLGR isolates. All isolates containing aac(6′)-aph(2″) were positive in long-PCR targeting Tn5281 and the probe hybridized with Tn5281 amplicons. The number of HLGR isolates of E. faecalis has increased considerably in Tehran hospitals. Tn5281 is the main cause of transmission of aac(6′)-aph(2″) to different isolates of E. faecalis in the hospitals studied.
Genetic analysis of theSalmonellatranscription factor HilA
Authors: Daly Rebecca A. , Lostroh C. Phoebe
Published: October 2008

HilA, a Salmonella transcription factor, activates the invF-1 and prgH promoters through binding to the HilA box, which contains 2 copies of a TTKHAT motif separated by a T centered at –45 relative to the start sites of transcription. The N-terminal 112 amino acids of HilA are similar to winged helix-turn-helix DNA binding/transcription activation domains (wHTH DBDs). The remaining 441 amino acids are not similar in sequence to any other well-characterized transcription factors. Here, we report that the wHTH DBD is essential for activation of both promoters, but amino acids 113–554 are only required for normal activation of invF-1. Some alanine substitutions in the putative α loop, which connects the recognition and positioning helices in wHTH DBDs, cause a loss-of-activation phenotype. A hilA allele encoding a protein with an alanine substituted for arginine at position 71 in the α loop has a loss-of-activation defect exclusively at the prgH promoter. The results suggest distinct roles for one or more domains formed by amino acids 113–554 and for arginine 71 in activation of the 2 promoters.
Alternative flagellar filament types in the haloarchaeon Haloarcula marismortui
Authors: Pyatibratov Michael G. , Beznosov Sergey N. , Rachel Reinhard , Tiktopulo Elizabeth I. , Surin Alexei K. , Syutkin Alexei S. , Fedorov Oleg V.
Published: October 2008

Many Archaea use rotation of helical flagellar filaments for swimming motility. We isolated and characterized the flagellar filaments of Haloarcula marismortui , an archaeal species previously considered to be nonmotile. Two Haloarcula marismortui phenotypes were discriminated—their filaments are composed predominantly of either FlaB or FlaA2 flagellin, and the corresponding genes are located on different replicons. FlaB and FlaA2 filaments differ in antigenicity and thermostability. FlaA2 filaments are distinctly thicker (20–22 nm) than FlaB filaments (16–18 nm). The observed filaments are nearly twice as thick as those of other characterized euryarchaeal filaments. The results suggest that the helicity of Haloarcula marismortui filaments is provided by a mechanism different from that in the related haloarchaeon Halobacterium salinarum , where 2 different flagellin molecules present in comparable quantities are required to form a helical filament.
Altered forest composition and soil properties of historic charcoal hearths in southeastern Pennsylvania
Authors: Mikan Carl J. , Abrams Marc D.
Published: October 2008

This study related age structure and composition of forests in southeastern Pennsylvania to edaphic properties caused by the activities of a local charcoal iron furnace from the late 18th to the late 19th century. Forests surrounding charcoal hearths were harvested on 20- to 30-year rotations to supply wood for charcoal production in earthmound kilns. Charcoal hearths were created by a recurring cycle of disturbance, including the removal of established vegetation, intense heat, and the deposition of charcoal. Thirty-eight hearths of Hopewell Furnace National Historic Site were examined to describe differences in vegetation relative to surrounding forests that have developed since the cessation of charcoal production in 1883. Hearth forests were significantly younger than surrounding forests, with lower tree density and basal area, decreased sapling and shrub abundance, and higher herbaceous cover. Compositional differences on charcoal hearths included decreased importance of several Quercus species and ericaceous shrubs and increased importance of Liriodendrontulipifera L. Results of this study indicated that the initial effect of charcoal production was the prevention of stump sprouting and a delay in recolonization following disturbance due to extreme soil physical and chemical properties. Failure of hearth seedlings to recruit into larger size classes, age–diameter relationships of Liriodendrontulipifera L. trees, and the failure of calcifuge species to reestablish similar cover on charcoal hearths suggested that unfavorable properties of charcoal soils continue to negatively affect long-term productivity. Relative to nonhearth soils, large, significant differences in soil pH, cation exchange capacity, base saturation, and exchangeable Ca, Mg, and K indicated that continuing inhibition of woody plants on charcoal hearths may be related to alterations in soil chemistry that have persisted for 110 years.
Modeling the effect of crown shedding and streamlining on the survival of loblolly pine exposed to acute wind
Authors: Hedden R.L. , Fredericksen T.S. , Williams S.A.
Published: October 2008

A simulation model using empirical data was developed to determine the effect of crown shedding and streamlining from stem and branch bending on the survival of mature loblolly pine (Pinustaeda L.) trees exposed to acute wind. Data collected from tree winching experiments were used to derive the forces necessary to cause stem failure. These data, combined with data on the vertical distribution of biomass and frontal surface area of sampled trees and hypothetical within-stand wind profiles, were used to calibrate models of static wind effect. Data collected on crown biomass, stem deflection, and branch bending were employed in the model to conduct a sensitivity analysis of the relative contribution of various crown adjustment mechanisms in preventing stem breakage or windthrow. Compared with the base-line model, which included no crown adjustment mechanisms, crown loss of 25% or greater provided the greatest protection against stem breakage or windthrow from forces generated by a hurricane winds of average strength (165 km/h), followed (in order of greatest to least protection) by stem bending, branch streamlining, and crown loss of 10%. However, at the highest wind velocities modeled (249 km/h), stem bending afforded greater protection against wind-generated mortality than 25% crown loss or branch streamlining, but not more than 50% crown loss. Generally, study trees most susceptible to windthrow were tall with a high center of gravity, large crown weight, and small stem taper.
Interpopulation differentiation of nuclear and chloroplast loci in white spruce
Authors: Furnier Glenn R. , Stine Michael
Published: October 2008

We compared the degree of differentiation among 22 populations of white spruce (Piceaglauca (Moench) Voss), a monoecious conifer, for six nuclear allozyme loci and a paternally inherited restriction fragment polymorphism in the chloroplast DNA (cpDNA). Estimates of FST (an F-statistic for the proportion of total variability due to differences among populations) were significantly higher for the cpDNA marker (0.147) than for the nuclear allozyme loci (mean = 0.037, range = 0.017–0.053), indicating greater differentiation for the cpDNA. Both cpDNA variants were observed in every population, and there was an east–west trend in the frequencies of these variants across North America. These observations may be explained by the different modes of inheritance of the cpDNA (paternal) and nuclear loci (biparental).
Using portable laser EDM for forest traverse surveys
Authors: Liu C.J.
Published: October 2008

A new electronic distance measurement (EDM) device that utilizes laser technology for tree measurement and surveying was used to study traverse surveys of forest stands. Experimental tests demonstrated that the laser EDM device afforded (1) an allowable angular closure error of 3°, (2) an average linear closure precision of 1/550 for a bidirectional traverse and of 1/470 for a unidirectional traverse, (3) an average traversing speed of 0.25 mi/h (0.40 km/h) for bidirectional traverses, and (4) an average surveying rate of 6 acres/h (2.4 ha/h). The study also showed that (1) the digital laser EDM device was 10 times more cost effective than the traditional analogous surveying equipment and (2) a unidirectional traverse is, on the average, 1.5 times more effective than a bidirectional traverse. Additional analyses revealed that the interior angle adjustment (IAA) procedure consistently altered the shape of the stand and changed the stand area. These findings led to several suggestions: (1) the laser EDM device should be adopted for forest stand traverse surveys because it is easy to use, accurate, and cost effective; (2) the routine of taking backsight in field measurement provides little gain in accuracy in stand area determination and should be exercised only when local magnetic interference is expected to adversely affect compass accuracy; and (3) the conventional practice of IAA prior to balancing the traverse should not be exercised, since this procedure has adverse effects on mapping and area determination.
Variability in early height growth rate of forest trees: implications for retrospective studies of stand dynamics
Authors: Palik Brian J. , Pregitzer Kurt S.
Published: October 2008

Retrospective studies of forest stand dynamics may rely on estimates of tree ages. In some of these studies, trees are aged near the stem base, while in other studies trees may be aged at breast height. An age correction may be added to breast-height ages in an attempt to account for average time to reach breast height and thus provide better estimates of total ages. Aging at breast height can provide estimates of stem and stand ages that are sufficient and appropriate for many studies of stand dynamics, for example, those focusing on the dynamics of canopy recruitment. However, the various aging methodologies will provide similar interpretations of actual stand age structures only if early height growth rates are not variable among stems, an assumption not likely to be true. Thus, aging at breast height, with or without a correction factor, may be inappropriate in studies that rely on accurate determination of tree establishment times. In the present study, variability of early height growth rates for several tree species common to Populusgrandidentata Michx. forests is quantified by determining the number of years to reach breast height. Interpretations of stand age structures and dynamics are made based on total tree ages, breast-height ages, and corrected breast-height ages. The results are compared to explore the implications of ignoring variability in early height growth rates when interpreting development of the stands. For the study populations, early height growth rates were highly variable. Some variability was accounted for by differences in understory tolerance, establishment times, and regenerative modes. Intolerant species establishing early grew faster than more tolerant, later establishing species. Sprout-origin stems grew faster, and had much less variable growth rates, than did seed-origin stems. In the understory, hardwood regeneration grew faster than pine regeneration. Even after accounting for these factors, early height growth rates were still variable. Within replicate plots, cumulative establishment distributions based on breast-height ages always differed from those based on total ages, leading to different interpretations of stand age structures. Cumulative establishment distributions based on breast-height ages corrected for aging height differed 44% of the time from those based on total ages. The timing of understory reinitiation, an important dynamic in even-aged forests, was determined using the three aging methods and compared. The timing of understory reinitiation based on breast-height ages differed significantly from that derived using total ages, while that derived using corrected breast-height ages did not differ from the latter. These results suggest that interpretations of stand age structures and past dynamics based on breast-height ages should be viewed cautiously if the objectives of a study require accurate estimates of tree establishment times.
The dendrochronological characteristics of alpine Larch
Authors: Colenutt M.E. , Luckman B.H.
Published: October 2008

Ring-width chronologies have been developed for alpine larch (Larixlyallii Pari.) at six tree-line sites in the Banff–Kananaskis area of the southern Canadian Rockies. Evaluation of all chronologies confirms that alpine larch ring-width series have higher mean sensitivities, lower autocorrelation, and greater common variance than series from other tree species growing at tree line in this area. Missing and very narrow rings created cross-dating difficulties at all sites but were most problematic for the sites along the Continental Divide. Up to 1% of the rings were missing from entire chronologies, but for specific years, up to 77% of the rings were missing at one site. Marker (narrow) rings were present at all sites for the years 1610, 1654, 1715, 1720, 1723, 1752, 1799, 1824, 1842, 1844, 1915, 1925, 1951, and 1971. Tree growth rates were reduced for the periods 1675–1710, 1815–1850, and 1960–1978 whereas increased growth occurred during 1650–1680, 1750–1800, 1850–1900, and 1920–1950. The only factor that could affect all sites over such a broad geographic area is climate. Principal components analysis indicated that the first eigenvector derived from the six chronologies accounted for 70.7% of their common variance and the first three components accounted for 91.6%. The high correlation between the six first principal component and standard chronologies suggested that either method may be used for standardizing tree-ring data from alpine larch.
Effects of regeneration methods on drought damage to newly planted Norway spruce seedlings
Authors: Nilsson Urban , Örlander Göran
Published: October 2008

A field experiment was established between 1989 and 1993 to study the effects of (i) the age of clearcuts on damage by pine weevils (Hylobiusabietis L.) and (11) competing vegetation on the survival and growth of planted Norway spruce (Piceaabies (L.) Karst.). On each of four sites Norway spruce seedlings were planted on 0 to 4-year-old clearcuts. Effects of mounding, herbicide and mowing, removal of slash, and seedling stock type were also investigated. As many seedlings suffered severely from a drought that affected southern Sweden in 1992, this study reports a separate analysis of mortality due to drough. From the middle of May until the beginning of July 1992, only negligible precipitation was recorded on all four sites. The biomass of ground vegetation was correlated with the age of the clearcut. On fresh and 1-year-old clearcuts, only negligible amounts of vegetation were found, whereas about 2 Mg•ha−1 of ground vegetation were found on 2- and 3-year-old clearcuts. Low soil water potentials were recorded on 2- and 3-year-old clearcuts but not on fresh clearcuts. There was no effect of the slash removal treatment on soil water potential, but there was a significant effect of the soil and vegetation treatments. Mounding and herbicide treatments increased the soil water potentials compared with untreated controls and mowed plots. Mortality by drought was higher for seedlings planted on old clearcuts than for seedlings planted on fresh ones. Mortality was reduced by mounding, but late planting increased the number of dead seedlings significantly. The mortality of containerized seedlings was considerably less than that of bare-root seedlings. On old clearcuts growth of seedlings planted on plots with no vegetation control (untreated control and mown plots) was less than that of seedlings planted on plots where transpiration by ground vegetation was reduced (herbicide and mounding).
Stand, species, and tree dynamics of an uneven-aged, mixed conifer forest type
Authors: McTague John P. , Stansfield William F.
Published: October 2008

Stand-level equations are presented that project future merchantable tree survival, pole-tree basal area, and sawtimber basal area. Total basal area (excluding ingrowth) is the sum of the pole-tree and sawtimber components. Ratio equations are used for eight species (seven softwoods and one hardwood) to compute the change in species abundance and species basal area over time. Individual-tree mortality is predicted with a logistic function, while individual-tree diameter growth is predicted as a function of stand and individual-tree attributes. The individual-tree and species-level equations are adjusted so that tree frequency and basal area are consistent with the stand-level projection equations. Total ingrowth is computed with a stand-level projection equation and is distributed with a parameter recovery method using the uniform distribution. The presence or absence of ingrowth for a given species is determined with a discriminant function, while the proportion of total ingrowth allocated to a species is predicted with a logistic function.
Infection of Populus tremuloldes by Hypoxylon mammatum ascospores through Saperda inornata gails
Authors: Ostry Michael E. , Anderson Neil A.
Published: October 2008

Branch galls resulting from oviposition wounds made by Saperdainornata Say on Populustremuloides Michx. were studied in relation to inoculation with Hypoxylonmammatum (Wahlenberg) J.H. Miller ascospores. The natural infection rate of galls in an aspen plantation in central Minnesota averaged 1.6% (range 0.8–2.6%) during a 4-year period. However, when S. inornata galls were inoculated with ascospores during a 3-year period, 9.1% (range 6.5–2.6%) of the branches became infected. When galls were inoculated with sterile water, 3.3% of the branches became infected, perhaps indicating that inoculum already was present in the galls. The average elapsed time from ascospore inoculation until the development of hypoxylon canker symptoms was 26 months. These results provide the first demonstration of canker development following inoculation of natural wounds on aspen with H. mammatum ascospores.
Evaluation of objective estimates of treatment efficacy for bigleaf maple
Authors: Knowe Steven A.
Published: October 2008

An evaluation of six objective estimators of treatment efficacy for bigleaf maple (Acermacrophyllum Pursh) was made on the basis of data from two herbicide screening studies. The estimators were evaluated for sensitivity to statistical comparison of treatment means. Evaluation was made on the basis of (i) overall mean and coefficient of variation for percent change in crown volume, as well as (ii) percent control based on regression-adjusted post-treatment crown height, (iii) crown diameter, (iv) crown profile, (v) crown area, and (vi) crown volume. Estimates of overall mean control were similar among the expressions of crown size, but the estimate based on change in crown volume was substantially lower. The coefficient of variation was smallest when control was calculated from crown height or crown profile and was largest for change in crown volume. Orthogonal contrasts indicated that control calculated from one- and two-dimensional expressions of crown size tended to be more sensitive to treatment differences than other expressions of crown size. Change in crown volume and control calculated from crown volume tended to be the least sensitive to treatment differences, resulting in rejection of the null hypothesis for fewer orthogonal contrasts. These results for bigleaf maple are consistent with the results obtained for several hardwood species in the southeastern United States.
Synchronic large-scale disturbances and red spruce growth decline
Authors: Reams Gregory A. , Van Deusen Paul C.
Published: October 2008

not available
INVESTIGATION OF 3D ACOUSTICAL EFFECTS USING A MULTIPROCESSING PARABOLIC EQUATION BASED ALGORITHM
Authors: CASTOR K. , STURM F.
Published: October 2008

A parallelized algorithm based on an existing 3D wide-angle parabolic equation model is developed to perform numerical simulations of underwater acoustic propagation on a massively parallel computer. The parallelization method used is a suitable two-level procedure: A frequency decomposition and a spatial decomposition of the calculations, which are respectively dedicated to reduce CPU times for broadband and cw signal propagation. The high-performance of the parallelized algorithm is examined for the 3D extension of the classical ASA wedge benchmark. CPU times are reported and both speedup and efficiency are analyzed. An investigation of significant 3D effects at higher frequencies and at longer propagation ranges than in earlier works [F. Sturm, J. Acoust. Soc. Am.117(3) (2005) 1058–1079] is performed with reasonable CPU times by using the new parallel algorithm. Further, the feasability of the procedure applied to a realistic oceanic environment problem involving both real sound speed profiles and bathymetry data sets is also illustrated.
A 2.5D TRACTION BOUNDARY ELEMENT METHOD FORMULATION APPLIED TO THE STUDY OF WAVE PROPAGATION IN A FLUID LAYER HOSTING A THIN RIGID BODY
Authors: ANTÓNIO J. , TADEU A. , MENDES P. AMADO
Published: October 2008

This paper models three-dimensional wave propagation around two-dimensional rigid acoustic screens, with minimal thickness (approaching zero), and placed in a fluid layer. Rigid or free boundaries are prescribed for the flat fluid surfaces.

The problem is computed using the Traction Boundary Element Method (TBEM), which is appropriate for modeling thin-body inclusions, overcoming the difficulty posed by the conventional direct Boundary Element Method (BEM).

The problem is solved as a summation of two-dimensional problems for different wave numbers along the direction for which the geometry does not vary. The source in each problem is a spatially sinusoidal harmonic line load. The influence of the horizontal boundaries of the fluid medium on the final wave field is computed analytically using appropriate 2.5D Green's functions for each model developed. Thus, only the boundary of the rigid acoustic screen needs to be discretized by boundary elements.

The computations are performed in the frequency domain and are subsequently inverse Fourier transformed to obtain time domain results. Complex frequencies are used to avoid aliasing phenomena in the time domain results.
AN ASSESSMENT OF THE PERFORMANCE OF GLOBAL OPTIMIZATION METHODS FOR GEO-ACOUSTIC INVERSION
Authors: SNELLEN MIRJAM , SIMONS DICK G.
Published: October 2008

Having available efficient global optimization methods is of high importance when going to a practical application of geo-acoustic inversion, where fast processing of the data is an essential requirement. A series of global optimization techniques are available and have been described in literature. In this paper three optimization techniques are considered, being a genetic algorithm (GA), differential evolution (DE), and the downhill simplex algorithm (DHS). The performance of these three methods is assessed using a test function, demonstrating superior performance of DE. Additionally, the DE optimal setting is determined. As a next step DE is applied for determining the geo-acoustic properties of the upper seabed sediments from simulated seabed reflection loss, indicating good DE performance also for real geo-acoustic inversion problems.
A MODAL ANALYSIS METHOD TO STUDY FLUID–STRUCTURE COUPLING IN HOLLOW PARTS OF A STRUCTURE
Authors: BESSET S. , JEZEQUEL L.
Published: October 2008

Complex structures often include hollow parts. These hollow parts constitute the skeleton of the structure and are largely responsible for its global behavior, hence the importance of analyzing them precisely. The method we propose in this paper is a modal method based on the modal analysis of elements of hollow parts. This method does not require nodal degrees of freedom on the boundaries between the elements: "modal" elements are created, and these elements can be assembled through modal mass and stiffness matrices in the same way as the finite element method. Thus, it is possible to choose the precision of the analysis by choosing the quantity of modes used in the modal analysis of the elements. We will study not only structural systems but also coupled fluid–structure systems, and our results will be compared with experimental tests.
Synchrotron Radiation
Authors: Hofmann A.
Published: October 2008

The physics of synchrotron radiation, undulator radiation, and free electron lasers is reviewed with an emphasis on the underlying physical principles and the experimental observables, such as the radiation spectrum, angular distribution, and radiation polarization.