bluuebunny/crossref_metadata_2025 huggingface dataset:
“Evil Habits” and “Personal Choices”: Assigning Responsibility for Health in the 20th Century
Authors: LEICHTER HOWARD M.
Published: December 2003

The 20th century began and ended with many of the nation's more affluent and better‐educated citizens in a near‐frenzied pursuit of better health through lifestyle modification. Americans sought and received health‐enhancing and disease‐preventing advice in books, newspapers, popular magazine articles, and government studies. They followed exercise regimes and bought self‐improvement paraphernalia from “medicine balls” to elliptical machines in order to learn “How to Avoid Heart Troubles” (Groedel 1901) and, even more ambitiously, to stay Forever Young (Berger 1989). Upton Sinclair alerted early 20th‐century Americans to the appalling conditions in the meatpacking industry (1906), and nearly a century later Eric Schlosser warned of the “Dark Side of the All‐American Meal” (2001). Finally, San Franciscans, fretting about the nutritional dangers to their children's health, began the last century by banning “roving pie vendors” who catered to the “habitual pie‐eating” habits of schoolchildren (Habitual Pie‐Eating Ruining Health of Children 1910) and began this century by prohibiting the sale of soft drinks and other unhealthy snacks on school campuses (Delgado 2003).
Identification of T‐cell epitopes of Porphyromonas gingivalis heat‐shock‐protein 60 in periodontitis
Authors: Choi J.‐I. , Kang H.‐S. , Park Y.‐M. , Kim S.‐J. , Kim U.‐S.
Published: December 2003

The heat shock proteins (hsp) of bacterial species are considered to be involved in regulating the autoimmune mechanism in human diseases due to the considerable homology of their sequences with human hsp. To elucidate how stress proteins contribute to the immunopathogenesis of periodontitis, mononuclear cells from gingival connective tissue of 10 periodontitis patients were simulated with Porphyromonas gingivalis hsp60. T‐cell lines reactive to P. gingivalis hsp60 were established from each patient to define T‐cell epitope specificities. Anti‐P. gingivalis IgG antibody titres were elevated in all patients. We could establish P. gingivalis hsp‐reactive T‐cell lines from gingival mononuclear cells that were mixtures of CD4+ and CD8+ cells. Of 108 overlapping synthetic peptides spanning the whole P. gingivalis hsp60 molecule, 10 peptides with epitope specificities for T‐cells were identified, and were identical to those reported be B‐cell epitopes in periodontitis.
Platelet responses and anaphylaxis‐like shock induced in mice by intravenous injection of whole cells of oral streptococci
Authors: Ohba M. , Shibazaki M. , Sasano T. , Inoue M. , Takada H. , Endo Y.
Published: December 2003

Intravenous injection of lyophilized whole cells of various oral streptococcal strains into muramyldipeptide (MDP)‐primed C3H/HeN mice induces rapid anaphylactoid shock. Here we examined the mechanism underlying this shock. In non‐primed mice, Streptococcus intermedius K‐213K (SiK213) and Streptococcus constellatus T21 (ScT21) produced little or no sign of shock. In MDP‐primed mice, SiK213 caused lethal shock, while ScT21 only had a weak effect. SiK213 induced decreases in blood platelets and 5‐hydroxytryptamine (5HT) preceding the shock, while the effects of ScT21 were weak. The SiK213‐induced 5HT decrease and shock were reduced by a complement‐C5 inhibitor. These results suggest that (i) streptococcal bacterial cells can induce rapid platelet responses, (ii) complement‐dependent degradation of platelets may be involved in streptococcus‐induced shock, (iii) the streptococcus‐induced platelet degradation or degranulation may occur largely in the systemic circulation, and (iv) platelets may play a role not only in infectious diseases caused by gram‐negative bacteria, but also in diseases caused by gram‐positive bacteria.
Characterization of two outer membrane protein antigens of Porphyromonas gingivalis that are protective in a murine lesion model
Authors: Ross B. C. , Czajkowski L. , Vandenberg K. L. , Camuglia S. , Woods J. , Agius C. , Paolini R. , Reynolds E. , Barr I. G.
Published: December 2003

Porphyromonas gingivalis is a key periodontal pathogen that has been implicated in the aetiology of chronic adult periodontitis. The aim of this study was to characterize two potential vaccine candidates (PG32 and PG33) identified from a previous genomic sequence analysis. Gene knockout studies suggested that these proteins play an important role in bacterial growth and are transcriptionally linked. Analysis of 14 laboratory and clinical isolates of P. gingivalis found that in all strains, both genes were present with a high level of conservation and that the two proteins were also expressed in vitro. Truncated recombinant PG32 and PG33 proteins were produced in Escherichia coli in an attempt to increase the solubility of the proteins while retaining their native conformation. While most of the truncated proteins remained insoluble, two truncated proteins showed good solubility and high levels of protection in the P. gingivalis murine lesion model and may be considered as potential vaccine candidates for further testing in models of human periodontal disease.
Two epithelial cell invasion‐related loci of the oral pathogen Actinobacillus actinomycetemcomitans
Authors: Li L. , Matevski D. , Aspiras M. , Ellen R. P. , Lépine G.
Published: December 2003

Two invasion‐related loci, apiA and the two‐gene operon apiBC, were isolated from the oral pathogen Actinobacillus actinomycetemcomitans UT32. apiA encodes a 32.5 kDa protein that migrates on SDS‐PAGE as a 101 kDa protein as detected by Western blot analysis or silver staining of an outer membrane‐enriched fraction of Escherichia coli transformants. E. coli expressing ApiA have a different phenotype than the host vector, in broth and on solid media, and a colony morphology that resembles that of fresh A. actinomycetemcomitans isolates. These E. coli transformants bound to chicken collagen type II, human collagen type II, III, V and fibronectin. apiB and apiC encode proteins of 130.1 and 70.6 kDa, respectively. ApiBC conferred on E. coli a slightly enhanced ability to bind to collagen type III. ApiA‐ and ApiB‐deficient mutants were constructed in A. actinomycetemcomitans. The ApiB‐mutant had 4‐fold diminished invasion of KB cells; the ApiA‐mutant had increased invasion. Both loci were found in all A. actinomycetemcomitans strains, although polymorphism was detected only for apiBC. The deduced sequences of these invasion‐related proteins are homologous to members of the YadA adhesin/invasin family.
Inactivation of srtA gene of Streptococcus mutans inhibits dextran‐dependent aggregation by glucan‐binding protein C
Authors: Igarashi T. , Asaga E. , Sato Y. , Goto N.
Published: December 2003

A sortase‐deficient mutant of Streptococcus mutans was prepared by insertional inactivation of a sortase gene (srtA). The srtA mutant was defective in cell wall‐anchoring of two surface proteins 200 and 75 kDa in size. A previous study has shown that the 200 kDa protein is a surface protein antigen PAc and that the sortase catalyzes cell wall‐anchoring of PAc in S. mutans. In this study another surface protein 75 kDa in size was examined by immunologic and physiologic methods. Western blot analysis with a specific antiserum showed that the 75 kDa protein was a surface protein, glucan‐binding protein C. The protein was overexpressed under a stress condition including a sublethal concentration of tetracycline. The srtA mutant cells also lost the ability of dextran‐dependent aggregation. These results suggest that the S. mutans sortase mediates cell wall‐anchoring of the glucan‐binding protein C and dextran‐dependent aggregation of this organism.
Physiologic actions of zinc related to inhibition of acid and alkali production by oral streptococci in suspensions and biofilms
Authors: Phan T.‐N. , Buckner T. , Sheng J. , Baldeck J. D. , Marquis R. E.
Published: December 2003

Zinc is a known inhibitor of acid production by mutans streptococci. Our primary objective was to extend current knowledge of the physiologic bases for this inhibition and also for zinc inhibition of alkali production by Streptococcus rattus FA‐1 and Streptococcus salivarius ATCC 13419. Zinc at concentrations as low as 0.01–0.1 mm not only inhibited acid production by cells of Streptococcus mutans GS‐5 in suspensions or in biofilms but also sensitized glycolysis by intact cells to acidification. Zinc reversibly inhibited the F‐ATPase of permeabilized cells of S. mutans with a 50% inhibitory concentration of about 1 mm for cells in suspensions. Zinc reversibly inhibited the phosphoenolpyruvate: sugar phosphotransferase system with 50% inhibition at about 0.3 mm ZnSO4, or about half that concentration when the zinc–citrate chelate was used. The reversibility of these inhibitory actions of zinc correlates with findings that it is mainly bacteriostatic rather than bactericidal. Zinc inhibited alkali production from arginine or urea and was a potent enzyme inhibitor for arginine deiminase of S. rattus FA‐1 and for urease of S. salivarius. In addition, zinc citrate at high levels of 10–20 mm was weakly bactericidal.
Alteration of gene expression profiles of peripheral mononuclear blood cells by tobacco smoke: implications for periodontal diseases
Authors: Ryder M. I. , Hyun W. , Loomer P. , Haqq C.
Published: December 2003

Alterations of the host response by tobacco smoke adversely affect the periodontium. In this study, we examined the effects of in vitro acute smoke exposure on changes in m‐RNA expression of primary peripheral mononuclear blood cells through microarray analysis. Mononuclear blood cells were isolated from four healthy non‐smokers and plated in culture wells. Half of the cells were then exposed to 5 min of tobacco smoke. Fluorescent c‐DNA probes were prepared from the linearly amplified m‐RNAs for each sample and hybridized to cDNA microarrays representing ∼30,000 human genes. Significant increases or decreases in m‐RNA gene expression between non‐smoke‐exposed and smoke‐exposed samples were identified by permutation t‐test, as implemented by the Significance Analysis of Microarrays software package. After smoke exposure, the expression of 90 genes with known function was significantly elevated and the expression of 19 genes with known function was significantly depressed. In addition, 18 upregulated and 26 downregulated transcripts were expressed sequence tags with little information available on function. Approximately 20 of the significantly elevated genes had previously been reported in the literature to be associated with periodontal pathogenesis (fold changes in parentheses). These included plasminogen activator (4.4), Heat Shock Protein (Hsp) 40 kD (2.2), thrombomodulin (4.2), cytochrome c (1.8), COX‐2 (2.6), interleukin‐1a (1.4), chemokine ligand 1 (3.8), cathepsin L (2.0), and calgranulin A (2.1). In addition, several significantly elevated genes not previously reported in the literature may also play a role in periodontal pathogenesis, and thus warrant further investigation. These include Diphtheria toxin receptor (heparin‐binding epidermal growth factor‐like growth factor) (7.8), Hsp 10 kDa (1.7), Hsp 105 kD (2.1), Hsp 70 kDa (1.6), and mitogen activated protein kinase 3 (1.5). Among the significantly depressed genes that may play a protective or destructive role in periodontal pathogenesis were interferon gamma receptor 2 (0.58) and chemokine receptor 2 (0.24). Our results may be of use in the search for the molecular mechanisms for the adverse effects of tobacco smoke on the host response.
A comparison of the antibacterial efficacies of essential oils against oral pathogens
Authors: Takarada K. , Kimizuka R. , Takahashi N. , Honma K. , Okuda K. , Kato T.
Published: December 2003

Cariogenic bacteria and periodontopathic bacteria are present in dental plaque as biofilms. In this study, we investigated the antibacterial effects of essential oils on the following oral bacteria:Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans,Fusobacterium nucleatum,Streptococcus mutans, andStreptococcus sobrinus. We tested manuka oil, tea tree oil, eucalyptus oil, lavandula oil, and romarinus oil and determined their minimum inhibitory concentration and minimum bactericidal concentration. The essential oils inhibited the growth of the bacteria tested, manuka oil being the most effective. Minimum bactericidal concentration values showed that lavandula oil acts bacteriostatically, and the remaining oils, bactericidally. Periodontopathic bacterial strains tested were killed completely by exposure for 30 s to 0.2% manuka oil, tea tree oil or eucalyptus oil. Tea tree oil and manuka oil showed significant adhesion‐inhibiting activity againstP. gingivalis. All the essential oils tested inhibited the adhesion ofS. mutans. This study showed that, among the essential oils tested, manuka oil and tea tree oil in particular had strong antibacterial activity against periodontopathic and cariogenic bacteria. From the viewpoint of safety, we also examined the effects of these essential oils on cultured human umbilical vein endothelial cells and found that, at a concentration of 0.2%, they had little effect on cultured cells.
Hemoglobin hydrolysis and heme acquisition by Porphyromonas gingivalis
Authors: Dashper S. G. , Cross K. J. , Slakeski N. , Lissel P. , Aulakh P. , Moore C. , Reynolds E. C.
Published: December 2003

Porphyromonas gingivalis has been implicated in the progression of chronic periodontitis, an inflammatory disease of the supporting tissues of the teeth. This bacterium is a gram‐negative, black‐pigmented, asaccharolytic anaerobe that relies on the fermentation of amino acids for the production of metabolic energy. The Arg‐ and Lys‐specific extracellular cysteine proteinases of P. gingivalis, RgpA, RgpB and Kgp have been implicated as major virulence factors. In this study we investigated the hydrolysis of human hemoglobin by whole cells of P. gingivalis W50 and the mutants W501 (RgpA−), W50AB (RgpA−RgpB−) and W50ABK (RgpA−RgpB−Kgp−) under strictly anaerobic conditions in a physiological buffer (pH 7.5) using mass spectrometric analysis. Incubation of P. gingivalis W50 with hemoglobin over a period of 30 min resulted in the detection of 20 hemoglobin peptides, all with C‐terminal Arg or Lys residues. The majority of the hemoglobin α‐ and β‐chain sequences were recovered as peptides except for two similar regions of the C‐terminal half of each chain, α(92‐127) and β(83‐120). The residues of the unrecovered sequences form part of the interface between the α‐ and β‐chains and an exposed surface area of the hemoglobin tetramer that may be involved in binding to P. gingivalis. P. gingivalis W501 (RgpA−) produced similar peptides to those seen in the wild‐type. All identified peptides from the hydrolysis of hemoglobin by the P. gingivalis W50AB (RgpA−RgpB−) mutant were the result of cleavage at Lys. The triple mutant W50ABK was unable to hydrolyze hemoglobin under the assay conditions used, suggesting that on whole cells the major cell surface activity responsible for hydrolysis of hemoglobin is from the RgpA/B and Kgp proteinases. However, the triple proteinase mutant W50ABK grew as well as the wild‐type in a medium containing hemoglobin as the only iron source, indicating that the RgpA/B and Kgp proteinases are not essential for iron assimilation from hemoglobin by P. gingivalis.
Comparative analysis of NK/T‐cell lymphoma and peripheral T‐cell lymphoma in Korea: Clinicopathological correlations and analysis of EBV strain type and 30‐bp deletion variant LMP1
Authors: Kim Ji Eun , Kim Young A. , Jeon Yoon Kyung , Park Sung Shin , Heo Dae Seog , Kim Chul Woo
Published: December 2003

Natural killer/T‐cell lymphoma (NKTL) and peripheral T‐cell lymphomas (PTCL) are prevalent in the Asian population and exhibit a high association with the Epstein–Barr virus (EBV). Moreover, differentiation of these two groups is often difficult and problematic. We investigated 35 cases of NKTL (22 nasal cases and 13 extranasal cases) and 30 cases of PTCL in terms of their clinical features, immunohistology, EBV positivity, EBV strain‐type polymorphism and latent membrane protein 1 (LMP1) deletion variant distribution. Eighteen cases (82%) of nasal NKTL and seven (54%) of extranasal NKTL showed EBV positivity by EBV in situ hybridization. Fifteen cases (50%) of PTCL revealed EBV positivity. EBV strain type A was predominant in NKTL (18:5), and EBV strain types A and B were distributed evenly in PTCL (6:6). EBV‐positive patients had significantly shorter survival than EBV‐negative patients (P < 0.05), and EBV positivity correlated with advanced clinical stage (P < 0.05). Patients harboring type A EBV showed slightly poorer prognoses than those having type B, though it was not obviously statistically different (P = 0.07). The LMP1 deletion variant was prevalent in both NKTL (three wild‐type LMP1, 15 deletion variants) and PTCL (three wild‐type LMP1, eight deletion variants, two coexistent forms) patients, but did not have prognostic impact. Our results indicate that EBV acts as a negative prognostic factor in NKTL and PTCL, and that the intrinsic properties of a specific viral strain might influence the clinical behavior of these diseases.
Phenotypic similarity and differentiation among sympatric cryptic species in a freshwater amphipod species complex
Authors: Wellborn Gary A. , Cothran Rickey D.
Published: December 2003

1. Cryptic species diversity poses evolutionary questions about its origin and maintenance, and ecological questions about the coexistence of seemingly identical species.

2. We examine patterns of morphological and life history differentiation in three sympatric cryptic species of freshwater amphipods within the Hyalella azteca species complex. These species are separated by extensive molecular evolution, but appear similar in phenotype. Species were collected from the littoral zone of a small kettle lake in Michigan, U.S.A., and identified to species by molecular genetic methods.

3. Two of the species were similar, differing only in female size, whereas the third was larger in body size and had larger clutches of smaller eggs than the other two. There were differences between the species also in pleon spine length and antennal segment number.

4. An analysis of allozyme variation among the cryptic species in three lakes suggests that the species are reproductively isolated within lakes.

5. We suggest that phenotypic similarity of these species is maintained by size‐selective predation by fish. The small, but statistically significant, differences in body size may form the axis for a tradeoff between resource exploitation and predator avoidance, a condition that can foster coexistence of phenotypically similar species.
Controls on periphyton biomass in heterotrophic streams
Authors: Bernhardt Emily S. , Likens Gene E.
Published: December 2003

1. Headwater streams of the Hubbard Brook Experimental Forest (HBEF) are typically characterised by a periphyton assemblage of low biomass and diversity. However, periphyton blooms have been observed following catchment deforestation experiments and occasionally during the annual spring thaw before canopy leaf‐out.

2. There is pronounced seasonal variation in both nutrient and light availability in HBEF streams. Stream water nitrogen (N) concentrations and light levels are higher before canopy leaf‐out and after leaf senescence and are lower during the growing season. Periphyton accrual rates also change seasonally; they are highest in spring prior to leaf‐out and significantly lower during summer and in autumn.

3. Periphyton biomass rarely responded positively to in‐situ experimental enrichment with nitrogen or phosphorus. In the summer, nutrient enrichment overall had no effect on periphyton biomass, while outside the growing season N enrichment had inhibitory effects on periphyton.

4. Despite these experimental results, surveys of ambient chlorophyll a concentrations in streams across the HBEF demonstrated no relationship between streamwater dissolved inorganic N or P concentrations and benthic chlorophyll a.

5. Our results suggest that HBEF periphyton communities are not closely regulated by nutrient availability, even during periods of high light availability. The inhibitory effects of nutrient enrichment outside the growing season are interesting, but further research is necessary to elucidate the mechanisms driving these responses.
Effects of small scale fluid motion on bacterial growth and respiration
Authors: Bergstedt Maria S. , Hondzo Miki M. , Cotner James B.
Published: December 2003

1. Laboratory experiments were conducted to investigate the effect of small‐scale turbulent motion on the growth and respiration of bacteria in an oscillating grid apparatus. The experiments were performed under a range of energy dissipation levels similar to those occurring in freshwater systems.

2. The results showed that small‐scale turbulent motion does have an effect on bacterial growth and respiration. A higher gradient in the dissolved oxygen time series, higher 5‐day biochemical oxygen demand values, increased bacterial abundance, increased bacterial specific respiration, higher bacterial growth rate and increased nutrient uptake were all observed when the energy dissipation rate in the water column was increased.

3. This has implications for traditional laboratory procedures that are used to characterise bacterial metabolic rates under stagnant fluid‐flow conditions, such as biochemical oxygen demand (BOD), which would be influenced by the effects of the small‐scale fluid motion inherent in aquatic environments. According to our results, BOD values in natural systems experiencing fluid motion would be higher than traditional bottle‐derived rates.
Growth‐ and feeding‐related isotopic dilution and enrichment patterns in young‐of‐the‐year yellow perch (Perca flavescens)
Authors: Murchie Karen J. , Power Michael
Published: December 2003

1. Isotopic signatures (δ15N and δ13C) from young‐of‐the‐year (YOY) yellow perch (Perca flavescens) were collected over the initial 4 month summer growing period from three separate and distinctive sites in northern Alberta, Canada. Data were analysed to test the hypotheses that there are within‐ and among‐population differences in the patterns of isotopic δ15N and δ13C change over the growing season, and that observed isotopic dilution and/or enrichment patterns were influenced by site‐specific physical and chemical factors.

2. Increases in δ15N relative to spawned egg masses were observed in immediate posthatch (emergent) YOY and attributed to enrichment associated with the assimilation of yolk during embryonic development.

3. Posthatch dilution of YOY δ15N signatures associated with ontogenetic dietary shifts from yolk to exogenous feeding and zooplanktivory to benthivory occurred at all sites and was associated at most sites with a concomitant increase in δ13C.

4. The rate and pattern of δ15N dilution and δ13C enrichment observed for the study populations varied between and within sites and depended on maternal trophic status and timing of ontogenetic dietary shifts, as determined by prey availability and site‐specific biogeochemical factors.

5. Comparisons of isotopic dilution patterns among species, using results from this study and literature‐derived values, indicated that dilution rates and patterns are species dependent and may vary in relation to key life‐history events.

6. Seasonal and spatial isotopic variability among populations and between species complicates field sampling. In particular, the connectivity to site‐specific conditions found here suggests that for locally resident juvenile fishes, spatial, as well as temporal variability must be included in isotopic sampling programmes designed to characterise littoral zone foodweb relationships.
Testing the ecological relevance of Daphnia species designations
Authors: Duffy Meghan A. , Tessier Alan J. , Kosnik Matthew A.
Published: December 2003

1. Molecular approaches have increasingly revealed hidden genetic structure within ecologically important species, leading to the creation of sibling species whose ecological relevance is often unclear. A prime example is Daphnia galeata mendotae, which was split into D. dentifera and D. mendotae based on differences at two allozyme loci.

2. In a set of lake populations in Michigan USA, we test the geographical and temporal consistency of the genetic structure underlying this species split. We also test the morphological relevance of this molecular variation and its ecological significance in lakes. In essence, we ask: does recognition of these new species provide valuable information for plankton ecologists?

3. We found that D. dentifera and D. mendotae represent morphologically and ecologically distinct forms that are distributed among lakes in non‐random fashion, which were remarkably stable over 6 years. Key differences between the species concern their body and head shape, vertical habitat use within lakes and distribution among lakes of different size. We hypothesise that these differences represent specialisation to habitats that differ in risk of invertebrate predation.

4. Reproductive barriers alone are insufficient to explain the pattern of genetic structure; in some lakes complete introgression is apparent. However, parent species and hybrids exhibit a stable co‐existence in many lakes, which suggests that ecological specialisation reinforces divergence within this taxon.
Saltcedar (Tamarix ramosissima) invasion alters organic matter dynamics in a desert stream
Authors: Kennedy Theodore A. , Hobbie Sarah E.
Published: December 2003

1. We investigated the impacts of saltcedar invasion on organic matter dynamics in a spring‐fed stream (Jackrabbit Spring) in the Mojave Desert of southern Nevada, U.S.A., by experimentally manipulating saltcedar abundance.

2. Saltcedar heavily shaded Jackrabbit Spring and shifted the dominant organic matter inputs from autochthonous production that was available throughout the year to allochthonous saltcedar leaf litter that was strongly pulsed in the autumn. Specifically, reaches dominated by saltcedar had allochthonous litter inputs of 299 g ash free dry mass (AFDM) m−2 year−1, macrophyte production of 15 g AFDM m−2 year−1 and algal production of 400 g AFDM m−2 year−1, while reaches dominated by native riparian vegetation or where saltcedar had been experimentally removed had allochthonous litter inputs of 7–34 g AFDM m−2 year−1, macrophyte production of 118–425 g AFDM m−2 year−1 and algal production of 640–900 g AFDM m−2 year−1.

3. A leaf litter breakdown study indicated that saltcedar also altered decomposition in Jackrabbit Spring, mainly through its influence on litter quality rather than by altering the environment for decomposition. Decomposition rates for saltcedar were lower than for ash (Fraxinus velutina), the dominant native allochthonous litter type, but faster than for bulrush (Scirpus americanus), the dominant macrophyte in this system.
Seasonal and inter‐annual scales of variability in phytoplankton assemblages: comparison of phytoplankton dynamics in three peri‐alpine lakes over a period of 28 years
Authors: Anneville O. , Souissi S. , Gammeter S. , Straile D.
Published: December 2003

1. A method based on hierarchical clustering and Bayesian probabilities is used to identify phytoplankton assemblages and analyse their pattern of occurrence and temporal coherence in three deep, peri‐alpine lakes. The hierarchical properties of the method allowed ranking by order of importance of the effects of changes related to climate and to human activity on the phytoplankton structure.

2. The three deep, peri‐alpine lakes (the Lower Zurich, Upper Zurich and Walen lakes) investigated in this study have been monitored since 1972. During that period they have undergone oligotrophication as a result of management programmes and they have been subject to similar meteorological effects that have led to higher water temperatures since 1988.

3. The phytoplankton assemblages of the most eutrophic lake (Lower Zurich) differ strongly from those observed in the two meso‐oligotrophic lakes. Local environmental conditions appear to be the main factor responsible for species composition and change in climate characterised by the warmer water temperatures observed since 1988 have had a major impact on the winter composition of the lower basin of Lake Zurich by promoting Planktothrix rubescens.

4. Some phytoplankton assemblages are found in all the lakes. Their patterns of occurrence display strong synchrony at the annual and/or inter‐annual scales. However, temporal coherence between the lakes sometimes also involves different assemblages.

5. The reduction in phosphorus had a great influence on long‐term changes in composition. In all three lakes, decreases in phosphorus are associated with a community characterised by some mixotrophic species or species adapted to low nutrient concentrations or sensitive to transparency. In the Lower Lake Zurich the decrease in phosphorus has also led to the development of species adapted to low light intensities.

6. Seasonal meteorological forcing has also induced synchronous changes, but the same assemblages are not necessarily involved, because the pool of the well‐placed candidate taxa that may develop is determined by the local environmental conditions, and mainly by phosphorus concentrations. In the most eutrophic lake, the seasonal pattern is characterised by a succession of more stages. However, the seasonal assembly dynamics involve the succession of species sharing common selective advantages that make them relatively stronger under these nutrient and light conditions.
Larval fish‐induced phenotypic plasticity of coexistingDaphnia: an enclosure experiment
Authors: Bernot Randall J. , Dodds Walter K. , Quist Michael C. , Guy Christopher S.
Published: December 2003

1. The indirect effects of predators on lower trophic levels have been studied without much attention to phenotypically plastic traits of key food web components. Phenotypic plasticity among species creates phenotypic diversity over a changing environmental landscape.

2. We measured the indirect effects of planktivorous larval walleye (Stizostedion vitreum) on phytoplankton biomass through their effects on the dominant herbivore species,Daphnia pulicariaandD. mendotae.

3. Fish had no effect on phytoplankton biomass or overallDaphniadensity. We observed a compensatory response to predation by functionally comparable species within a trophic level in the form of shifting dominance and coexistence ofDaphniaspecies. We hypothesized that this phenotypically plastic response to predation decoupled a potential trophic cascade in this freshwater pelagic system.Daphnia pulicariadensity decreased over time with fish predation, butD. mendotaedensity increased over time with fish predation.

4. Phenotypically plastic life history trait shifts and reproductive rates differed between species in fishless and fish enclosures, accounting for population trends.Daphnia pulicariawere also proportionally higher in walleye larvae stomachs than in the enclosures, indicating that walleye preferred to feed onD. pulcariaoverD. mendotae. The resultant shift in dominance may partially explain the overall benign effect of fish on grazers and supports the hypothesis that trophic level diversity can decouple a trophic cascade.
Selective grazing by adults and larvae of the zebra mussel (Dreissena polymorpha): application of flow cytometry to natural seston
Authors: Dionisio Pires L. M. , Jonker R. R. , Van Donk E. , Laanbroek H. J.
Published: December 2003

1. Selective grazing of adults and larvae of the zebra mussel (Dreissena polymorpha) on phytoplankton and detritus from both laboratory cultures and natural seston was quantified using flow cytometry.

2. Mean clearance rate of adult zebra mussels was higher on a mixture of the green alga Scenedesmus and the cyanobacterium Microcystis than when Scenedesmus was offered as single food, suggesting selective feeding by the mussels.

3. Feeding on lake seston both adults and larvae showed a higher clearance rate on phytoplankton than on detritus particles, suggesting that zebra mussels select for phytoplankton. Furthermore, it was noted that adults preferred seston particles in the 0–1 and 30–100 μm size ranges.

4. In our study, zebra mussels did not discriminate against cyanobacteria, and our results indicate that they may even ingest them preferentially.
Deep-level transient spectroscopy study on double implanted n+–p and p+–n 4H-SiC diodes
Authors: Mitra Souvick , Rao Mulpuri V. , Papanicolaou N. , Jones K. A. , Derenge M. , Holland O. W. , Vispute R. D. , Wilson S. R.
Published: December 2003

Planar n+–p and p+–n junction diodes, fabricated in 4H-SiC epitaxial layers using a double-implantation technology (a deep-range acceptor followed by a shallow-range donor implantation and vice versa), are characterized using capacitance deep-level transient spectroscopy (DLTS) to detect deep levels, which may influence device electrical performance. Either Al or B was used as the acceptor, while N or P was used as the donor, with all implants performed at 700 °C and annealed at 1600–1650 °C with an AlN protection cap. Different traps were observed for the various dopants, which are believed to be related to different impurity-defect complexes. A trap at ∼EV+0.51 eV was observed in nitrogen-implanted samples, while an acceptor trap at ∼EV+0.28 eV and a donor trap at ∼EC−0.42 eV were observed in Al-implanted samples. A prominent boron-related D-center trap at ∼EV+0.63 eV is seen in the DLTS spectra of B-implanted diodes. In diodes with implanted phosphorus, three traps at ∼EV+0.6 eV, EV+0.7 eV, and EV+0.92 eV, are seen, which are not observed for implantations of other species.
Theory of a room-temperature silicon quantum dot device as a sensitive electrometer
Authors: Vincent J. K. , Narayan V. , Pettersson H. , Willander M. , Jeppson K. , Bengtsson L.
Published: December 2003

We consider theoretically the use of a room-temperature silicon quantum dot based device for electrometer applications. The low power device includes two split gates that quantize the electronic energy levels in the emitter and collector regions. The base consists of a silicon quantum dot buried in silicon dioxide. The small size of the dot and quantization of the states in the leads combined to allow the device to operate at room temperature. The nonlinear current–voltage characteristics can be significantly altered by small changes to the potential of the split gates. Power dissipation in the device therefore changes with the split gate voltage, and this can be exploited in electrometer applications. A simple model of the power dissipated when the device is part of a microwave resonant inductor-resistor-capacitor tank circuit suggests that large changes in device power can be achieved by changing the gate voltage, thereby forming a measurable signal. We also demonstrate that the power dissipation in the device changes as the base width is varied, and that the current through the device increases exponentially with a decrease in base width.
All-silicon polarizing filters for near-infrared wavelengths
Authors: Wu Qi Hong , De Silva Lakshman , Arnold Matthew , Hodgkinson Ian J. , Takeuchi Eric
Published: December 2003

We discuss the design and fabrication of optical filters that are transparent to a preferred linear polarization, but are partially or substantially reflective to the orthogonal linear polarization. The filters are fabricated by depositing thin films of form-birefringent silicon onto silicon wafers using the serial bideposition method. Characteristic curves that are presented for the in-plane principal refractive indices np and ns of the porous films as functions of vapor impingement angle facilitate critical aspects of the filter design. These include matching of a p principal index and an s principal index for films deposited at different angles, and realization of p and s principal indices that satisfy the antireflection condition for the silicon substrate in air.
Determination of lattice parameter and of N lattice location in InxGa1−xNyAs1−y/GaAs and GaNyAs1−y/GaAs epilayers
Authors: Bisognin G. , De Salvador D. , Mattevi C. , Berti M. , Drigo A. V. , Ciatto G. , Grenouillet L. , Duvaut P. , Gilet P. , Mariette H.
Published: December 2003

We have used an experimental strategy that, combining nuclear reaction analysis and Rutherford backscattering spectrometry both in random and channeling geometry, allowed an accurate quantification of the total amount of N in InxGa1−xNyAs1−y/GaAs and GaNyAs1−y/GaAs epitaxial systems (0.038<x<0.044, 0.015<y<0.045), and a precise localization of nitrogen atoms into the lattice. All N atoms were found on substitutional positions. This information was then exploited to correlate the relaxed lattice parameter of the epilayers obtained by high-resolution x-ray diffraction to the N concentration, by taking into account the elasticity theory, allowing a verification of the validity of Vegard’s rule in the whole range of investigated N concentrations for both alloys. The effect of N incorporation on the lattice parameter has been found to be the same both for ternary and quaternary alloys.
Near-field infrared imaging of molecular changes in cholesteryl oleate by free electron laser infrared ablation
Authors: Masaki Tatsuhiro , Goto Kazuya , Inouye Yasushi , Kawata Satoshi
Published: December 2003

We have applied infrared near-field scanning optical microscopy (IR–NSOM) to enable evaluation of detailed molecular changes in cholesteryl oleate, a primary cause of arteriosclerosis. In our IR–NSOM, a wide wavelength range of 2.9–6.7 μm is achieved by use of an optical parametric amplifier and an apertured cantilever. IR irradiation from a free-electron laser (FEL) tuned to a 5.75 μm wavelength induced molecular structural changes and caused cholesteryl oleate to decompose to cholesterol and fatty acids in the FEL irradiated areas. The IR–NSOM images at two different wavelengths, 5.75 and 5.3 μm, with a 2 μm apertured cantilever probe successfully identified areas of molecular change in cholesteryl oleate beyond the diffraction limit of IR microspectroscopy. In-depth molecular structure changes were also evaluated by the IR–NSOM and we demonstrated that the FEL irradiation induced subsurface molecular structure changes throughout cholesteryl oleate in the irradiated areas.
Polymer beads in microtubule-filled composites: Effects on length distributions and permittivities
Authors: Chiou Bor-Sen , Lankford Andrew R. , Schoen Paul E.
Published: December 2003

The effects of adding poly(methylmethacrylate) beads to tubule-filled composites were examined in terms of changes in tubule distribution and dielectric properties of the composites. The beads had an average diameter of 51±29 μm, whereas the copper-coated tubules, which were shaped like hollow cylinders and derived from a phospholipid template, had an average length of 30±22 μm and an average diameter of 1 μm. Incorporating a small amount of beads increased the permittivity value of the composite, but adding more beads resulted in a dramatic decrease in the permittivity value. In fact, a permittivity maximum appeared at around 5 vol % beads for various tubule loadings. The results could be explained in terms of volume exclusion and decreased tubule length effects. At low bead loadings, the volume exclusion effect dominated as the tubules were pushed closer together, resulting in a higher permittivity value. At higher bead loadings, the tubules were broken into shorter pieces and this became the dominant effect. Consequently, the shorter tubules formed fewer conducting pathways and the permittivity declined in value. In addition, the De Loor model for composites containing a dielectric matrix and conductors as fillers correctly predicted a permittivity maximum and provided the best fit to the permittivity data.
Excessive Balmer line broadening in microwave-induced discharges
Authors: Jovičević S. , Ivković M. , Konjević N. , Popović S. , Vušković L.
Published: December 2003

Results of a hydrogen Balmer line-shape study on microwave-induced plasma discharges operated with pure hydrogen and with argon–hydrogen or helium–hydrogen mixtures are reported. Plasma is generated in a rectangular or coaxial microwave cavity in two separate experiments. In both cases, the emission profiles of the Balmer lines did not show excessive broadening as reported by Mills et al. [J. Appl. Phys. 92, 7008 (2002)].
Influence of ambient on hydrogen release from p-type gallium nitride
Authors: Myers S. M. , Vaandrager B. L. , Wampler W. R. , Seager C. H.
Published: December 2003

Mechanisms of H release from Mg-doped, p-type GaN were investigated in vacuum, in N2 and O2 gases, and in electron–cyclotron-resonance N2 plasmas. Replacing grown-in protium with deuterium (D) and employing sensitive nuclear-reaction analysis allowed the retained concentration to be followed quantitatively over two decades during isothermal heating, illuminating the kinetics of controlling processes. Oxidation attending the O2 exposures was monitored through nuclear-reaction analysis of O18. N2 gas at atmospheric pressure increases the rate of D release appreciably relative to vacuum. The acceleration produced by O2 gas is much greater, but is diminished in later stages of the release by oxidation. The N2 plasma employed in these studies had no resolvable effect. We argue that surface desorption is rate controlling in the D release, and that it occurs by D–D recombination and the formation of N–D and O–D species. Our results are quantitatively consistent with a theoretical model wherein the bulk solution is in equilibrium with surface states from which desorption occurs by processes that are both first and second order in surface coverage.
Electronic structure and interband transitions of semiconducting carbon nanotubes
Authors: D’yachkov P. N. , Hermann H.
Published: December 2003

Band structure of semiconducting (0,n) carbon nanotubes (coefficients 0, n are the indices of the two-dimensional primitive lattice vectors of the graphene lattice) is calculated in terms of the linear augmented cylindrical wave method. The results are used to correlate the first and second minimum direct energy differences E11 and E22 between the singularities of the conduction and valence bands with the nanotube diameter d. Significant deviations from the equation Eii∼d−1, i=1,2, are observed. The gap energies E11(d−1) and E22(d−1) are oscillating functions that gradually decay to zero as d−1 goes to zero, reach their maximum at d−1 between 0.08 and 0.1 Å−1, and decrease abruptly at d−1>0.1 Å−1. There are two branches of the dependence of Eii on d even for nanotubes with the same chirality. This ambiguity complicates the determination of the structure of nanotubes on the basis of optical gaps, but, on the other hand, it opens the opportunity to classify experimental data more specifically.
Extreme ultraviolet emission spectra of highly ionized xenon and their comparison with model calculations
Authors: Böwering N. , Martins M. , Partlo W. N. , Fomenkov I. V.
Published: December 2003

Xenon spectra involving emission from ion species of Xe7+ to Xe12+ were analyzed for a plasma focus discharge developed for extreme ultraviolet lithography. Low and higher resolution spectra were recorded in the 8–21 nm wavelength region for different operating conditions and different He–Xe gas mixtures. The spectra have been compared with Hartree–Fock calculations. The modeling included the distribution of the various xenon ion levels at a given electron equilibrium temperature and plasma opacity effects. Spectral analysis showed that the 4d–5p transition arrays are fairly well separated in wavelength for the ions Xe8+ to Xe11+. Good agreement between experiment and calculations was obtained for line positions and intensities, in particular, for the wavelength region at around 13.5 nm.
Joining of stainless-steel specimens with nanostructured Al/Ni foils
Authors: Wang J. , Besnoin E. , Duckham A. , Spey S. J. , Reiss M. E. , Knio O. M. , Weihs T. P.
Published: December 2003

We describe the joining of stainless-steel specimens at room temperature using free-standing Al/Ni foils as local heat sources for melting AuSn solder layers. The foils contain many nanoscale layers of Al and Ni that react exothermically, generating a self-propagating reaction. The heats, velocities, and products of the reactions are described, and the microstructure and the mechanical properties of the resulting joints are characterized. Increasing the foil thickness, and thereby increasing the total heat released, can improve the strength of the joints until foil thickness reaches 40 μm. For thicker foils, the shear strength is almost constant at 48 MPa, compared to 38 MPa for conventional solder joints. The higher strength is due to finer microstructures in the solder layers of reactive joints. A numerical study of heat transfer during reactive joining and experimental results suggest that the solder layers need to melt completely and remain molten for at least 0.5 ms to form a strong joint.
High-pressure synthesis and ferroelectric properties in perovskite-type BiScO3–PbTiO3 solid solution
Authors: Inaguma Yoshiyuki , Miyaguchi Atsushi , Yoshida Masashi , Katsumata Tetsuhiro , Shimojo Yoshiro , Wang Ruiping , Sekiya Tadashi
Published: December 2003

Stabilization of a perovskite-type solid solution (1−x) PbTiO3–x BiScO3 with x⩾0.45 was demonstrated by high-pressure synthesis, and the phase diagram and the ferroelectric properties of the solid solution were investigated. The crystal symmetry of the perovskite subcell change in turn from tetragonal, to rhombohedral, to pseudocubic, to monoclinic, and then to triclinic as x increases. It was found that the tetragonal, rhombohedral, and pseudocubic phases are ferroelectric, while the monoclinic phase is not. In the morphotropic phase boundary in the vicinity of x=0.37 between tetragonal and rhombohedral phases, the maximum electromechanical coupling factor and the minimum coercive electric field were just like those observed in other Pb-based ferroelectric perovskites. In addition, relaxor behavior in the dielectric constant was observed in the vicinity of x=0.5.
Characterization of GaAs/AlGaAs quantum wires by means of longitudinal photoconductivity
Authors: Saraydarov M. , Donchev V. , Germanova K. , Wang X. L. , Kim S. J. , Ogura M.
Published: December 2003

We have carried out an original study of longitudinal photoconductivity (PC) of undoped GaAs/AlGaAs V-grooved quantum wires (QWRs) by measuring the PC along the wire direction. The PC spectrum reveals several peak structures superimposed on a smooth background, the latter being related to the GaAs substrate. Some of these structures are connected with the QWRs. This is confirmed by the observed dependence of the PC spectrum on the exciting light polarization and by comparing this spectrum with photoluminescence and photoluminescence excitation spectra measured on a similar sample. A theoretical identification of the peak structures is given by calculating the optical transition energies of the studied QWRs in frames of the envelope function approximation. An original approach, based on the infrared preillumination of the sample, is proposed to reduce the contribution of the GaAs substrate to the PC, in this way favoring the QWR spectral structures.