bluuebunny/crossref_metadata_2025 huggingface dataset:
Coxiella burnetiiInhibits Activation of Host Cell Apoptosis through a Mechanism That Involves Preventing CytochromecRelease from Mitochondria
Authors: Lührmann Anja , Roy Craig R.
Published: August 2007

Coxiella burnetiiis an obligate intracellular pathogen and the etiological agent of the human disease Q fever.C. burnetiiinfects mammalian cells and then remodels the membrane-bound compartment in which it resides into a unique lysosome-derived organelle that supports bacterial multiplication. To gain insight into the mechanisms by whichC. burnetiiis able to multiply intracellularly, we examined the ability of host cells to respond to signals that normally induce apoptosis. Our data show that mammalian cells infected withC. burnetiiare resistant to apoptosis induced by staurosporine and UV light.C. burnetiiinfection prevented caspase 3/7 activation and limited fragmentation of the host cell nucleus in response to agonists that induce apoptosis. Inhibition of bacterial protein synthesis reduced the antiapoptotic effect thatC. burnetiiexerted on infected host cells. Inhibition of apoptosis inC. burnetii-infected cells did not correlate with the degradation of proapoptotic BH3-only proteins involved in activation of the intrinsic cell death pathway; however, cytochromecrelease from mitochondria was diminished in cells infected withC. burnetiiupon induction of apoptosis. These data indicate thatC. burnetiican interfere with the intrinsic cell death pathway during infection by producing proteins that either directly or indirectly prevent release of cytochromecfrom mitochondria. It is likely that inhibition of apoptosis byC. burnetiirepresents an important virulence property that allows this obligate intracellular pathogen to maintain host cell viability despite inducing stress that would normally activate the intrinsic death pathway.
Analysis of the In Vitro Transcriptional Response of Human Pharyngeal Epithelial Cells to AdherentStreptococcus pneumoniae: Evidence for a Distinct Response to Encapsulated Strains
Authors: Bootsma Hester J. , Egmont-Petersen Michael , Hermans Peter W. M.
Published: August 2007

Infection of the human host byStreptococcus pneumoniaebegins with colonization of the nasopharynx, which is mediated by the adherence of bacteria to the respiratory epithelium. Several studies have indicated an important role for the pneumococcal capsule in this process. Here, we used microarrays to characterize the in vitro transcriptional response of human pharyngeal epithelial Detroit 562 cells to the adherence of serotype 2 encapsulated strain D39, serotype 19F encapsulated strain G54, serotype 4 encapsulated strain TIGR4, and their nonencapsulated derivatives (Δcps). In total, 322 genes were found to be upregulated in response to adherent pneumococci. Twenty-two genes were commonly induced, including those encoding several cytokines (e.g., interleukin 1β [IL-1β] and IL-6), chemokines (e.g., IL-8 and CXCL1/2), and transcriptional regulators (e.g., FOS), consistent with an innate immune response mediated by Toll-like receptor signaling. Interestingly, 85% of genes were induced specifically by one or more encapsulated strains, suggestive of a capsule-dependent response. Importantly, purified capsular polysaccharides alone had no effect. Over a third of these loci encoded products predicted to be involved in transcriptional regulation and signal transduction, in particular mitogen-activated protein kinase signaling pathways. Real-time PCR of a subset of 10 genes confirmed the microarray data and showed a time-dependent upregulation of, especially, innate immunity genes. The downregulation of epithelial genes was most pronounced upon adherence of D39Δcps, as 68% of the 161 genes identified were repressed only by this nonencapsulated strain. In conclusion, we identified a subset of host genes specifically induced by encapsulated strains during in vitro adherence and have demonstrated the complexity of interactions occurring during the initial stages of pneumococcal infection.
Differential Contribution of BacterialN-Formyl-Methionyl-Leucyl- Phenylalanine and Host-Derived CXC Chemokines to Neutrophil Infiltration into Pulmonary Alveoli during Murine Pneumococcal Pneumonia
Authors: Gauthier Jean-François , Fortin Andrée , Bergeron Yves , Dumas Marie-Christine , Champagne Marie-Eve , Bergeron Michel G.
Published: August 2007

Despite the development of new potent antibiotics,Streptococcus pneumoniaeremains the leading cause of death from bacterial pneumonia. Polymorphonuclear neutrophil (PMN) recruitment into the lungs is a primordial step towards host survival. Bacterium-derivedN-formyl peptides (N-formyl-methionyl-leucyl-phenylalanine [fMLP]) and host-derived chemokines (KC and macrophage inflammatory protein 2 [MIP-2]) are likely candidates among chemoattractants to coordinate PMN infiltration into alveolar spaces. To investigate the contribution of each in the context of pneumococcal pneumonia, CD1, BALB/c, CBA/ca, C57BL/6, and formyl peptide receptor (FPR)-knockout C57BL/6 mice were infected with 106or 107CFU of penicillin/erythromycin-susceptible or -resistant serotype 3 or 14S. pneumoniaestrains. Antagonists to the FPR, such as cyclosporine H (CsH) and chenodeoxycholic acid, or neutralizing antibodies to KC and MIP-2 were injected either 1 h before or 30 min after infection, and then bronchoalveolar lavage fluids were obtained for quantification of bacteria, leukocytes, and chemokines. CsH was effective over a short period after infection with a high inoculum, while anti-CXC chemokine antibodies were effective after challenge with a low inoculum. CsH prevented PMN infiltration in CD1 mice infected with either serotype 3 or 14, whereas antichemokine antibodies showed better efficacy against the serotype 3 strain. When different mouse strains were challenged with serotype 3 bacteria, CsH prevented PMN migration in the CD1 mice only, whereas the antibodies were effective against CD1 and C57BL/6 mice. Our results suggest that fMLP and chemokines play important roles in pneumococcal pneumonia and that these roles vary according to bacterial and host genetic backgrounds, implying redundancy among chemoattractant molecules.
ITS sequence variation supports the hybrid origin ofMalus toringoidesHughes
Authors: Feng Ting-Ting , Zhou Zhi-Qin , Tang Jian-Min , Cheng Ming-Hao , Zhou Shi-Liang
Published: August 2007

Malus toringoides (Rehd.) Hughes was suggested to have originated from hybridization between Malus transitoria Schneid. and Malus kansuensis Rehd., followed by repeated backcrossing to one of the putative parents. In the present study, the sequence information of the internal transcribed spacer (ITS) of nuclear ribosomal DNA (nrDNA) was used to re-examine the origin of this species. A total of 69 accessions from three natural populations (Maerkang, Xiaba and Kehe, Aba Autonomous Region, Sichuan, China) of M. toringoides and 10 accessions of its putative parents were analyzed. Using Malus angustifolia (Ait.) Michx., Malus ioensis (Wood) Britt. and Malus doumeri Chev. as outgroups, our phylogenetic analysis of the ITS sequences of M. toringoides and its putative parents showed that M. toringoides was not monophyletic, and two different types of ITS sequences which were obtained from each of the six accessions of M. toringoides were found to have clustered separately with those of the two putative parent species on the gene tree. A comparison of the sequence variation between M. toringoides and its putative parents revealed an additive variation pattern of ITS sequences in the putative hybrid species. These results are consistent with the previous morphological and amplified fragment length polymorphism (AFLP) data which suggested that M. toringoides was of hybrid origin. Our ITS data provide new molecular evidence for the hybrid origin hypothesis of M. toringoides and these results are of great importance for future study on hybridization, polyploid speciation and evolution of the genus Malus Miller.
Flowering and seedling production of understory herbs in old-growth forests affected by 1980 tephra from Mount St. Helens
Authors: Zobel Donald B. , Antos Joseph A.
Published: August 2007

To determine the variation in flowering among species and the contribution of flowering to the recovery of forest herbs, we counted the flowering shoots, vegetative shoots, and first-year seedlings in old-growth forests affected by tephra from the 1980 eruption of Mount St. Helens. Using permanent 1 m2 plots with either undisturbed tephra or with the tephra removed, we obtained 2–9 years of flowering data during 1980–2000 for six sites that received 2–15 cm of tephra. Flowering was infrequent for most species. Most of the 12 commonest species had 2%–4% of their shoots flowering (range 0%–15%). Among growth forms, deciduous nonclonal species flowered most. Flowering percentage increased with plant density; thus microsites favorable for growth were also favorable for flowering. Flowering varied considerably among sampling years. Incidence of flowering was higher on shallow than on deep tephra, and higher on natural tephra than in cleared plots. Seedlings were more common on shallow than on deep tephra. The 20-year increase in shoot density on tephra (ratio of 2000 to 1981 values) was positively related among species to the number of seedlings produced per previous-year flowering shoot. Our results indicate how species vary in the quantity and timing of flowering and also in their reliance on seedling establishment versus clonal growth for population increase following disturbance.
Seedling emergence and survival of Warea carteri (Brassicaceae), an endangered annual herb of the Florida Scrub
Authors: Weekley Carl W. , Menges Eric S. , Quintana-Ascencio Pedro F.
Published: August 2007

Seedling emergence and survival to flowering are critical processes in the life history of annual plants. We evaluated the importance of year and habitat on seedling emergence and the effects of year, habitat, timing of seedling emergence, and seedling density on survival of Warea carteri Small, an annual mustard endemic to Florida scrub. We tagged 1329 seedlings in 78 permanent 0.25 m2 quadrats in two habitats (scrub and disturbed) between 1999 and 2002 and followed seedlings monthly. Most (>80%) seedling emergence occurred between September and December. Emergence peaked 2 months earlier and was more variable in disturbed sites than in scrub. Seedling survival among years ranged from 3.5% to 12.0%. Seedling density varied from 1 to 75 per 0.25 m2 quadrat, with an overall median of 6.0. Survival was not density dependent. Median age at flowering ranged from 11.7 to 15.2 months, with late season recruits most likely to survive to flowering. Warea carteri recruits like a winter annual but flowers like a summer annual. Its delayed germination and a 12–15 month life span contribute to population cycling. Complete reproductive failure in unfavorable years, high seed production in favorable years, low rates of seed germination, and a persistent seed bank are consistent with predictions for an annual species in a variable habitat.
A simple method to assess macrofungal sporocarp biomass for investigating ecological change
Authors: Tóth B.B. , Feest A.
Published: August 2007

The methodologies used for studying macrofungal communities are an eclectic assemblage of many different and unstandardized approaches. In this study we propose a simple, nondestructive but still informative method to assess fungal sporocarp biomass in forested areas. We use the number of fruiting bodies found in the surveyed plot, and data on cap diameter of the species from the literature to calculate a cap area index. We show that this index very strongly correlates with the measured total dry mass of the species obtained from the same plot. We point out that the cap area index provides a more accurate estimation of the epigeous fungal sporocarp biomass than do the species sporocarp numbers. This new methodology allows the spatiotemporal distribution of a fungal community in an ecosystem to be followed. Since sporocarp production responds much more sensitively to environmental changes than does the fine-root vegetative ectomycorrhizal community, it may more quickly reflect whether an ecosystem has been perturbed. It will also allow us to collect data on saprotrophic species. A sporocarp survey can be useful for detecting early changes in the habitat and environment, and give an easily applicable method for conservation biology and ecosystem management.
Rice phosphate transporters associated with phosphate uptake in rice roots colonised with arbuscular mycorrhizal fungi
Authors: Glassop Donna , Godwin Rosamond M. , Smith Sally E. , Smith Frank W.
Published: August 2007

The completed rice-genome sequence was screened with a known inorganic phosphate (Pi) transporter sequence to reveal a family of 13 Pi transporters. This family can be used for studies into Pi acquisition and translocation throughout the plant. Plants that form symbiotic associations with arbuscular mycorrhizal (AM) fungi are of particular interest with respect to Pi acquisition because of their ability to utilize both direct and fungal pathways of uptake. Localization of transcripts of two Pi transporters by real-time RT-PCR and in situ hybridization were conducted in rice subjected to low Pi, high Pi, and AM colonization. One Pi transporter, ORYsa;Pht1;13, was detected in rice roots under all growth conditions. ORYsa;Pht1;11 was only expressed in roots colonized by AM fungi. Antisense RNA probes of ORYsa;Pht1;11 localized to cortical cells containing arbuscules and hyphal coils, formed by Glomus intraradices Schenck and Smith and Scutellospora calospora (Nicolson and Gerdemann) Walker and Sanders, respectively. Localization of the ORYsa;Pht1;13 probes was similar to that observed for ORYsa;Pht1;11 in colonized rice roots. This research proposes that at least two rice Pi transporters are involved in acquiring Pi via AM fungi, emphasising the complexity of Pi acquisition in plants with access to two Pi uptake pathways.
Climate warming and active layer thaw in the boreal and tundra environments of the Mackenzie Valley
Authors: Woo Ming-ko , Mollinga Michael , Smith Sharon L
Published: August 2007

The variability of maximum active layer thickness in boreal and tundra environments has important implications for hydrological processes, terrestrial and aquatic ecosystems, and the integrity of northern infrastructure. For most planning and management purposes, the long-term probability distribution of active layer thickness is of primary interest. A robust method is presented to calculate maximum active layer thickness, employing the Stefan equation to compute phase change of moisture in soils and using air temperature as the sole climatic forcing variable. Near-surface ground temperatures (boundary condition for the Stefan equation) were estimated based on empirical relationships established for several sites in the Mackenzie valley. Simulations were performed for typically saturated mineral soils, overlain with varying thickness of peat in boreal and tundra environments. The probability distributions of simulated maximum active layer thickness encompass the range of measured thaw depths provided by field data. The effects of climate warming under A2 and B2 scenarios for 2050 and 2100 were investigated. Under the A2 scenario in 2100, the simulated median thaw depth under a thin organic cover may increase by 0.3 m, to reach 1 m depth for a tundra site and 1.6 m depth for a boreal site. The median thaw depth in 2100 is dampened by about 50% under a 1 m thick organic layer. Without an insulating organic cover, thaw penetration can increase to reach 1.7 m at the tundra site. The simulations provide quantitative support that future thaw penetration in permafrost terrain will deepen differentially depending on location and soil.
Limnology, sedimentology, and hydrology of a jökulhlaup into a meromictic High Arctic lake
Authors: Lewis Ted , Francus Pierre , Bradley Raymond S
Published: August 2007

A large ice-dammed lake drained catastrophically into Lake Tuborg, Ellesmere Island, beginning on 25 July 2003. Limnological, sedimentological, and hydrological parameters were recorded before, during, and after this event. For several weeks prior to the jökulhlaup, water overtopped the ice-dammed lake and flowed into Lake Tuborg's freshwater basin. A shallow sill separates the freshwater basin from a larger, deeper basin containing ~25 PSU (practical salinity units) salt water. The sill blocked underflows from entering the saltwater basin before the jökulhlaup. The ice-dammed lake drained completely and catastrophically when englacial or subglacial conduits developed, and a glacier portal formed 980 m from the Lake Tuborg shore, marking the beginning of the jökulhlaup. The level of Lake Tuborg increased by 7.6 m in 84 h. This jökulhlaup is the largest known to have occurred in the High Arctic, and the largest witnessed in Canada since 1947. Strata of very cold water flowed above the chemocline for about 14 km, from the sill to the southwest end of the lake. The cold strata turbulently mixed with underlying salt water, allowing for saltwater flocculation of suspended sediment, causing rapid settling. The saltwater layer very slightly freshened and cooled. Close to the sill, near-surface sediments derived from the jökulhlaup are coarse and laminated; however, no erosion occurred toward the distal end of the lake, where a fining upward unit with a coarse base was deposited.
Barite (BaSO4) biomineralization at Flybye Springs, a cold sulphur spring system in Canada's Northwest Territories
Authors: Bonny Sandy M , Jones Brian
Published: August 2007

The Flybye Springs, Northwest Territories, consist of 10 active vents and numerous small seeps that discharge sulphide- and barium-rich spring waters at an average temperature 8.5 °C. Oxidation of sulphide to sulphate drives precipitation of stellate and platy barite microcrystals in the proximal flow paths. Downstream, and in vent- and tributary-fed ponds, barite is precipitated among streamer and mat forming colonies of sulphur-tolerant microbes, including Thiothrix, Beggiatoa, Thioploca, Chromatium, Oscillatoria, fungi (dominantly Penicillium), and unicellular sulphate reducing bacteria. These microbes mediate barite saturation by adjusting redox gradients and via passive adsorption of barium ions to cell surfaces and extracellular polymeric substances. Passive biomineralization produces barite laminae in floating microbial mats, nanometric coatings, and micrometric encrustations around microbial cells and filaments, and local permineralization of Thiothrix, Beggiatoa, and Oscillatoria outer cell walls. Intracellular barium enrichment and (or) metabolic sulphur oxidation may be important to "active biomineralization" that produces nanometric barite globules on the tips of fungal hyphae, barite-filled cell cavities in Beggiatoa and Thiothrix, and baritized sulphur globules. Degradation of biomineralized cells generates detrital "microfossils," including barite tunnels, layered cylinders, solid cylindrical grains and chains of barite beads. The diversity of inorganic and biomineralized barite in the Flybye Springs flow path highlights the influence of ambient chemistry, microbial metabolism, and cellular structure on barite solubility and on the taphonomy of microfossils preserved in barite.
Centrum growth patterns provide evidence for two small taxa of Hiodontidae in the Cretaceous Dinosaur Park Formation
Authors: Newbrey Michael G , Wilson Mark V.H , Ashworth Allan C
Published: August 2007

Disarticulated centra recovered from the Campanian Dinosaur Park Formation (Cretaceous) are used to describe hiodontid age, growth, and longevity. Previous studies of Cretaceous centrum morphology have shown only one morphotype. However, growth characteristics can be used to test the one-taxon hypothesis. Age and growth characteristics indicate that Cretaceous hiodontids were shorter-lived (i.e., 7 years) and significantly smaller than extant Hiodon. The fossil centra also exhibit two significantly different growth patterns. Initially it was predicted that two factors could explain the presence of the two growth patterns: (1) sexual size dimorphism, and (2) variation in centrum size from multiple species. Sexual size dimorphism did not produce the two growth patterns because (1) H. alosoides maximum total length is significantly correlated with temperature, and (2) the paleotemperature in the depositional environment fluctuated approximately 6 °C mean annual temperature resulting in continuous growth variation. Concerning the second factor, the coefficient of variation (CV) observed in the Cretaceous centrum size data (0.23 CV) is 22% greater than that of the two extant species of Hiodon combined (0.18 CV) suggesting that at least two species of hiodontids were present in the Dinosaur Park Formation. The distribution of sizes of the smaller Cretaceous centra is not different from one extant species but is significantly different from two species suggesting that three taxa were not present.
A new paraclupeid fish (Clupeomorpha, Ellimmichthyiformes) from a muddy marine pro-delta environment: middle Cenomanian Dunvegan Formation, Alberta, Canada
Authors: Hay Michael J , Cumbaa Stephen L , Murray Alison M , Plint A Guy
Published: August 2007

A black marine mudstone in allomember A of the middle Cenomanian Dunvegan Formation, Alberta, yielded a well-preserved, deep-bodied fish skeleton attributable to a new genus and species, Tycheroichthys dunveganensis, in the Paraclupeidae (Clupeomorpha, Ellimmichthyiformes). This new taxon appears most closely related to members of the subfamily Paraclupeinae, which includes largely freshwater and estuarine or marginal marine species known from South and Central America and China. The Dunvegan Formation represents a large delta complex deposited in the Western Interior Seaway at about 65°N, where mean sea water temperature may have been about 10 °C. The specimen was found about 60 km from the contemporaneous shoreline, and, in life, apparently inhabited a shallow, muddy pro-delta environment characterized by high turbidity and variable salinity. The fish may have died when it was engulfed by brackish floodwater that also introduced suspended mud that rapidly buried the body, preventing physical disarticulation of the skeleton. River outflow probably produced a salinity- and density-stratified water column that limited oxygen transfer to the sea floor, leading to dysaerobic bottom water and an absence of scavengers. High terrestrial phytodetrital content of the sediment also favoured anaerobic conditions that limited bacterial decay.
Alpine glacial geology of the Tablelands, Gros Morne National Park, Newfoundland
Authors: Osborn Gerald , Spooner Ian , Gosse John , Clark Doug
Published: August 2007

Controversy persists in western Newfoundland regarding Pleistocene, particularly Late Wisconsinan, glacial ice volumes. Independently, a set of alpine glacial deposits on the flanks of the Tablelands in Gros Morne National Park has attracted much attention but little scrutiny. In this study, cosmogenic nuclide dating of the alpine deposits places some limits on post-late glacial maximum (LGM) ice dynamics in the vicinity of the Tablelands, a plateau bounded on the northeast by Trout River Gulch. Small valleys incised into the flanks of the Tablelands are floored with a diamict that contains both till and ice-contact deposits. Rock glaciers rest on the diamict, and rock glacierization also has affected talus lining the south wall of Trout River Gulch. A small moraine rests in the Devil's Punchbowl cirque. The cirque moraine, lobate deposits below the cirque moraine, rock glaciers, and a colluvial veneer overlying the till in the small valleys have cosmogenic 36Cl ages as old as either ca. 20 or 15 ka, depending on what erosion rate is assumed, indicating that these bodies are Late Wisconsinan in age but post-date the local LGM. Trout River Gulch was deglaciated early and perhaps did not contain active ice even at the LGM, but previous work shows that ice was streaming seaward both north of Trout River Gulch and south of the Tablelands even as the gulch lay relatively ice free.
Capillary instability of a streaming fluid-core liquid jet underself-gravitating forces
Authors: Radwan A E , Elmahdy E E
Published: August 2007

The stability criterion of a fluid cylinder (density ρ(1)) embedded in a different fluid (density ρ(2)) is derived and discussed. The model is capillary unstable in the domain 0 < x < 1 as m = 0 where x and m are the axial and transverse wave numbers, while it is stable in all other domains. The densities ratio ρ(2) / ρ(1) decreases the unstable domains but never suppress them. The streaming increases the unstable domains. Gravitationally, in m = 0 mode the model is unstable in the domain 0 < x < 1.0668 as ρ(2) < ρ(1), while as ρ(2) = ρ(1) it is marginally stable but when ρ(2) > ρ(1) the model is purely unstable for all short and long wavelengths. In m ≠ 0 modes, the self-gravitating model is neutrally stable as ρ(1) = ρ(2), ordinarily stable as ρ(2) < ρ(1), but is purely unstable as ρ(2) > ρ(1). The streaming destabilizing effect makes the self-gravitating instability worse and shrinks the stable domains. The stability analysis of the model under the combined effect of the capillary and self-gravitating forces is performed analytically and verified numerically. When ρ(2) < ρ(1) the capillary force and the axial flow have destabilizing influences but the ratio of the densities ρ(2) / ρ(1) has a stabilizing effect on the gravitating instability. If ρ(1) = ρ(2), the streaming is destabilizing but the capillary force is strongly stabilizing and could suppress the gravitational instability. When ρ(2) > ρ(1) the capillary force improves the gravitational instability and creates domains of much stability and moreover the instability of the self-gravitating force disappears in several cases of axisymmetric disturbances. PACS No.: 47.17+e
Boundary-layer flow of a micropolar fluid on a continuous flatplate moving in a parallel stream with uniform surface heat flux
Authors: Ishak A , Nazar R , Pop I
Published: August 2007

The laminar boundary-layer flow of a micropolar fluid on a fixed or continuously moving flat plate with uniform surface heat flux is investigated. The plate is assumed to move in the same oropposite direction to the free stream. The resulting system of nonlinear ordinary differential equations is solved numerically using the Keller-box method. Numerical results are obtained for the skin-friction coefficient and the local Nusselt number as well as the velocity, microrotation, and temperature profiles for some values of the governing parameters, namely, the velocity ratio parameter, material parameter, and Prandtl number. The results indicate that dual solutions exist when the plate and the free stream move in the opposite directions.PACS No.: 47.15.Cb
Algebraic dynamic study of geometric phase for a homonuclear linear spincluster
Authors: Chen X -X , Xue J
Published: August 2007

A homonuclear linear [Formula: see text] coupling spin cluster with the middle particle driven by an external time-dependent magnetic field is investigated by using the method of algebraic dynamics. The exact analytical solutions of the time-dependent Schrodinger equation of the spin cluster system are derived and employed to study the geometric phase. An alternative expression of the geometric phase in each eigenstate is obtained. It is shown that the geometric phase is related to the external magnetic-field parameter θ (the angle between the magnetic field and the Z axis) and the effective coupling strength Jn. Based on the relation, how the geometric phase depends on the coupling strength Jn in different reducible subspace is discussed.PACS Nos.: 33.20.Wr, 03.65.Fd, 03.65.Vf
Approximate three-dimensional analysis of rectangular barrette–soil–cap interaction
Authors: Lei G H , Hong X , Shi J Y
Published: August 2007

Rectangular barrettes are increasingly being used to support large-size and heavy-duty structures, but the interaction among barrettes, soil, and cap has rarely been studied theoretically. This paper presents an approximate three-dimensional semi-analytical method for the analysis of load–displacement behaviour of single barrettes, barrette groups, and barrette–soil–cap interaction systems. A unique feature of a barrette, which distinguishes it from a circular pile, is its nonaxisymmetrical mechanical behaviour. To take into account this feature, both the barrette–soil and the cap–soil interfaces are discretized. Mindlin's solution is adopted to define the load–displacement relationship of the soils next to the barrette and the cap. By assuming the deformation compatibility at the barrette–soil and cap–soil interfaces, the load–displacement relationship of the soils is incorporated into the static force equilibrium conditions in the interior of the barrette and cap structures. In this way, governing equations in finite difference form are derived for obtaining the load–displacement response of the barrette–soil–cap system. The proposed method is verified by comparing the calculated results for a group of square piles using other existing methods. In addition, some factors such as barrette shape, barrette spacing, and barrette group layout and finite-layer depth, which influence the response of the barrette–soil–cap system, are investigated.Key words: elasticity, foundations, numerical modelling, piles, theoretical analysis.
Cyclic shear stress degradation and post-cyclic behaviour from sand–steel interface direct shear tests
Authors: Mortara Giuseppe , Mangiola Antonio , Ghionna Vito Nicola
Published: August 2007

The sliding interaction between sand and structural materials is involved in many geotechnical applications and is particularly important for the derivation of the shaft capacity of piles. Such interaction develops principally at the interface between the sand mass and the structural surface, and the comprehension of such interaction can be analysed through soil–structure interface tests. In particular, by using a modified version of the interface direct shear apparatus, that is, the constant normal stiffness direct shear apparatus, the friction characteristics of the interface and the role of the soil deformability on the experimental results can be studied. This paper focuses on the stress degradation occurring in these types of tests when cyclic loading is applied on sand–steel interfaces. Also, the post-cyclic response is analysed and compared to the response under monotonic conditions.Key words: interface, sand, shear stress, cyclic loading, stress degradation.
Assessing the mechanical stability of horizontal boreholes in coal
Authors: Hawkes C D
Published: August 2007

Horizontal wells are used in some geological settings in the petroleum industry to produce methane from coal seams. Horizontal directional drilling is used in the mining industry to enhance the effectiveness of coal degasification procedures and to aid in the delineation of coal reserves. Coals tend to be mechanically weak, hence they are prone to borehole instability related problems during drilling, completion, and production operations. This paper includes a review of the mechanical properties of selected coals and provides two empirical cross-plots that can be used for estimating coal strength from index tests and geophysical logs. Linear elastic borehole stability models are demonstrated to be appealing because they are easily implemented, require a minimum of input data, and are well suited to rapid parameter sensitivity analyses. Using experience obtained drilling vertical wells in a given setting, a methodology is described for calibrating linear elastic models to provide realistic borehole stability predictions. Furthermore, as demonstrated using a western Canadian example (a shallow well in the Ardley coal zone), relatively simple elastoplastic models can be used effectively for borehole stability analyses. The important effects of filter cake, coal depth, and rock strength anisotropy are demonstrated with two different elastoplastic models.Key words: borehole stability, coal, methane, directional drilling, strength, stress.
Numerical modelling of the hydrogeological and geomechanical behaviour of a large slope movement: the Triesenberg landslide (Liechtenstein)
Authors: François B , Tacher L , Bonnard Ch. , Laloui L , Triguero V
Published: August 2007

Using advanced hydrogeological and geomechanical finite element modelling, it has been possible to model the mechanical behaviour of a large slope movement, the Triesenberg landslide. This slope is located along the Rhine valley in the Principality of Liechtenstein and covers an area of around 5 km2, which includes two villages. Pore-water pressure fields calculated by the hydrogeological model were used as input for the geomechanical model. The results obtained through numerical simulation agree fairly well with field measurements of peak velocity, spatial and temporal distribution of velocity, and total displacements. Such results were obtained using a modified Cam-Clay elastoplastic constitutive model for which the required material parameters were obtained through careful geotechnical tests. These finite element models were carried out in two and three dimensions to gradually improve the understanding of the physical phenomena governing the hydrogeological conditions and the movements of the slope.Key words: landslides, slope movement, hydromechanical coupling, elastoplasticity, numerical modelling.
Preventing surface deposition of chromium with asphalt caps at chromite ore processing residue sites: a case study
Authors: Henry Karen S , Petura John C , Brooks Steven , Dentico Steven , Kessel Stephen A , Harris Mark
Published: August 2007

Caps were constructed on chromite ore processing residue (COPR) sites in the Kearny, New Jersey, area between 1989 and 1994 to prevent human exposure to hexavalent chromium (Cr(VI)). The caps comprise geotextile overlain by 100 mm of dense graded aggregate (DGA) and 100 mm of hot mix asphalt (HMA). Prior to constructing these "composite asphalt caps" (CACs), Cr(VI) was sometimes deposited on surface soils as chromate (salts) during evaporative periods. We initially thought the geotextile and DGA acted as a capillary barrier, stopping capillary water rise, but site inspection revealed that the DGA and geotextile were too moist to perform this function. Further study included a literature review, DGA capillary rise estimates, in situ measurement of soil-water content over 7 months at a representative COPR site, and numerical modeling of matric suction gradients induced by evaporation. The collective results reveal that the CACs eliminate upward matric suction gradients from the COPR–soil through the DGA, thereby precluding surface chromate deposition. Even during evaporative periods, the low unsaturated hydraulic conductivity of the HMA restricts upward movement of moisture and soluble chromate from underlying COPR–soil. In contrast, there are almost always upward matric suction gradients in uncapped COPR–soil.Key words: capillary rise, chromite ore processing residue, chromate, hexavalent chromium, composite asphalt cap, evaporation.
Before the Frank Slide
Authors: Cruden David M , Martin C Derek
Published: August 2007

The Frank Slide occurred on the east limb of the Turtle Mountain Anticline, which was thrust up along the folded and splayed Turtle Mountain Fault. Easterly dipping, Paleozoic limestones and dolomites then rested on sheared, weaker, Mesozoic clastic rocks and coal strata. Cordilleran glaciers steepened the eastern flank of Turtle Mountain but left buttressing kame moraines. These were eroded by the Crowsnest River, which was pushed against Turtle Mountain between its North and South Peaks by the growth of the alluvial fan of Gold Creek. Blairmore Group mudstones and shales beneath the moraines were susceptible to toppling. Photographs of the east slope of Turtle Mountain before the Frank Slide show disturbed vegetation, uneven topography, steep slopes, and rock fall deposits, all consistent with active slope movements. The Frank Slide may have been triggered by the freezing of melting snow in rock joints and by coal mining. Our calculations show that, while individual stopes may have been unstable, the mine pillars and the coal mine itself were stable. Numerical simulations of the coal mining in the Frank Mine suggest mining reduced the strength of the east slope of Turtle Mountain by less than 10% before the Frank Slide.Key words: Rocky Mountains, Frank Slide, coal mining, river erosion, toppling.
Rock mass response model for circular openings
Authors: Sari Dursun
Published: August 2007

The main parameters affecting the failure and deformation state of the rock mass around a circular opening are the level of vertical and horizontal in situ stresses, the characteristics of the rock mass, the diameter of the opening, and the support pressure. The influence of all these parameters on the stress-induced final deformations around circular openings was investigated by a finite difference based two-dimensional numerical simulation for both hydrostatic and nonhydrostatic stress field conditions. From the results of the parametric studies, the variation of tunnel strain versus the ratio of uniaxial compressive strength of the rock mass to in situ vertical stress and the ratio of radial support pressure to in situ vertical stress for fair quality and poor quality rock masses was statistically analysed. As a result of the three-dimensional nonlinear regression analysis and surface curve fitting process by means of a large number of models, a best-fit model with the best correlation with these dimensionless parameters was proposed for calculating tunnel strains and ground response curves. Specific charts were created to highlight the influence of parameters on the deformation response of the openings to various support pressures.Key words: numerical modelling, circular openings, ground response curve, finite difference, FLAC.
MAPPING COMPLICATED SURFACES ONTO A SPHERE
Authors: RAHI SAHAND JAMAL , SHARP KIM
Published: August 2007

A method for mapping a closed, triangulated surface of genus 0 onto the unit sphere was developed using a parameterization based on spherical coordinates analogous to latitude and longitude combined with Mercator scaling. The algorithm was tested on 77 protein and DNA surfaces and produce correct (bijective) mappings. The mappings produce relatively uniform distortion, as judged by angular criteria, and by distribution of octant areas, thus facilitating the graphical analysis of these surfaces. An application to the analysis and comparison of electrostatic surface potentials in the active sites of three serine proteases is presented.
REGION INTERVISIBILITY IN TERRAINS
Authors: MOET ESTHER , VAN KREVELD MARC , VAN OOSTRUM RENÉ
Published: August 2007

A polyhedral terrain is the graph of a continuous piecewise linear function defined over the triangles of a triangulation in the xy-plane. Two points on or above a terrain are visible to each other if the line-of-sight does not intersect the space below the terrain. In this paper, we look at three related visibility problems in terrains. Suppose we are given a terrain T with n triangles and two regions R1 and R2 on T, i.e., two simply connected subsets of at most m triangles. First, we present an algorithm that determines, for any constant ∊ > 0, within O(n1+∊m) time and storage whether or not R1 and R2 are completely intervisible. We also give an O(m3n4) time algorithm to determine whether every point in R1 sees at least one point in R2. Finally, we present an O(m2n2 log n) time algorithm to determine whether there exists a pair of points p ∈ R1 and q ∈ R2, such that p and q see each other.
ON THE EXPECTED SIZE OF THE 2D VISIBILITY COMPLEX
Authors: EVERETT HAZEL , LAZARD SYLVAIN , PETITJEAN SYLVAIN , ZHANG LINQIAO
Published: August 2007

We study the expected size of the 2D visibility complex of randomly distributed objects in the plane. We prove that the asymptotic expected number of free bitangents (which correspond to 0-faces of the visibility complex) among unit discs (or polygons of bounded aspect ratio and similar size) is linear and exhibit bounds in terms of the density of the objects. We also make an experimental assessment of the size of the visibility complex for disjoint random unit discs. We provide experimental estimates of the onset of the linear behavior and of the asymptotic slope and y-intercept of the number of free bitangents in terms of the density of discs. Finally, we analyze the quality of our estimates in terms of the density of discs.
A MONOTONIC CONVOLUTION FOR MINKOWSKI SUMS
Authors: MILENKOVIC VICTOR , SACKS ELISHA
Published: August 2007

We present a monotonic convolution for planar regions A and B bounded by line and circular arc segments. The Minkowski sum equals the union of the cells with positive crossing numbers in the arrangement of the convolution, as is the case for the kinetic convolution. The monotonic crossing number is bounded by the kinetic crossing number, and also by the maximum number of intersecting pairs of monotone boundary chains, which is typically much smaller. We give a Minkowski sum algorithm based on the monotonic convolution. The running time is O (s + nα(n) log (n) + m2), versus O (s + n2) for the kinetic algorithm, with s the input size and with n and m the number of segments in the kinetic and monotonic convolutions. For inputs with a bounded number of turning points and inflection points, the running time is O (sα(s) log s), versus Ω(s2) for the kinetic algorithm. The monotonic convolution is 37% smaller than the kinetic convolution and its arrangement is 62% smaller based on 21 test pairs.
AGGREGATIVE MOVEMENT AND FRONT PROPAGATION FOR BI-STABLE POPULATION MODELS
Authors: MAINI PHILIP K. , MALAGUTI LUISA , MARCELLI CRISTINA , MATUCCI SERENA
Published: August 2007

Front propagation for the aggregation-diffusion-reaction equation [Formula: see text] is investigated, where f is a bi-stable reaction-term and D(v) is a diffusion coefficient with changing sign, modeling aggregating-diffusing processes. We provide necessary and sufficient conditions for the existence of traveling wave solutions and classify them according to how or if they attain their equilibria at finite times. We also show that the dynamics can exhibit the phenomena of finite speed of propagation and/or finite speed of saturation.
ANISOTROPIC STABLE LEVY COPULA PROCESSES — ANALYTICAL AND NUMERICAL ASPECTS
Authors: FARKAS WALTER , REICH NILS , SCHWAB CHRISTOPH
Published: August 2007

We consider the valuation of derivative contracts on baskets of risky assets whose prices are Lévy-like Feller processes of tempered stable type. The dependence among the marginals' jump structure is parametrized by a Lévy copula. For marginals of regular, exponential Lévy type in the sense of Ref. 7 we show that the infinitesimal generator [Formula: see text] of the resulting Lévy copula process is a pseudo-differential operator whose principal symbol is a distribution of anisotropic homogeneity. We analyze the jump measure of the corresponding Lévy copula processes. We prove that the domains of their infinitesimal generators [Formula: see text] are certain anisotropic Sobolev spaces. In these spaces and for a large class of Lévy copula processes, we prove a Gårding inequality for [Formula: see text].

We design a wavelet-based dimension-independent tensor product discretization for the efficient numerical solution of the parabolic Kolmogorov equation [Formula: see text] arising in valuation of derivative contracts under possibly stopped Lévy copula processes. In the wavelet basis, diagonal preconditioning yields a bounded condition number of the resulting matrices.
MOTION OF GAS BUBBLES, CONSIDERED AS MASSLESS BODIES, AFFORDING DEFORMATIONS WITHIN A PRESCRIBED FAMILY OF SHAPES, IN AN INCOMPRESSIBLE FLUID UNDER THE ACTION OF GRAVITATION AND SURFACE TENSION
Authors: LOZINSKI ALEXEI , ROMERIO MICHEL V.
Published: August 2007

A model allowing to describe motion and coalescence of gas bubbles in a liquid under the action of gravitation and surface tension is proposed. The shape of the bubbles is described by a pre-defined family of mappings, for example ellipsoids with a fixed volume and the effects of the gas motions inside the bubbles are neglected. The motion of a bubble is obtained in a Lagrangian form using the D'Alembert principle of virtual works. The set of equations is numerically solved with the help of the fictitious domain technique in which the Navier–Stokes equations in the domain formed by both fluid and gas are considered. The equations governing the bubbles motion are imposed by introducing Lagrange multipliers on the bubbles boundaries. Numerical results in 2D and 3D are presented.
BLACK–SCHOLES–MERTON IN RANDOM TIME: A NEW STOCHASTIC VOLATILITY MODEL WITH PATH DEPENDENCE
Authors: OSTROVSKY DMITRY
Published: August 2007

A generalized Black–Scholes–Merton economy is introduced. The economy is driven by Brownian motion in random time that is taken to be continuous and independent of Brownian motion. European options are priced by the no-arbitrage principle as conditional averages of their classical values over the random time to maturity. The prices are path dependent in general unless the time derivative of the random time is Markovian. An explicit self-financing hedging strategy is shown to replicate all European options by dynamically trading in stock, money market, and digital calls on realized variance. The notion of the average price is introduced, and the average price of the call option is shown to be greater than the corresponding Black–Scholes price for all deep in- and out-of-the-money options under appropriate sufficient conditions. The model is implemented in limit lognormal random time. The significance of its multiscaling law is explained theoretically and verified numerically to be a determining factor of the term structure of implied volatility.
PUBLIC DEBT MANAGEMENT AND FOREIGN CURRENCY DENOMINATED BONDS
Authors: CECCACCI SILVIA , MARCHESIANI ALESSANDRO , PECCHI LORENZO
Published: August 2007

Foreign-currency denominated securities are introduced in a stochastic model à la Missale [13]. It is shown that the percentage share of this bond type, as compared to total debt, is an increasing function of the covariance between the output and the rate of depreciation, but it may or may not be a decreasing function of the volatility of the rate of depreciation.
MARGIN TRADING THROUGH HYPER TIMELINE
Authors: NG SIU-AH
Published: August 2007

We consider a model of margin trading based on the hyperfinite timeline. Using only elementary nonstandard analysis we are able to derive explicit formulas for the expected margin call time and loss. Further margin trading strategy is studied and an application to pricing barrier option is given. We prove a generalization of the Catalan numbers which forms the combinatoric basis of our results and should be of independent interest.
FUZZY SETS IN POLITICAL SCIENCE: AN OVERVIEW
Authors: NURMI HANNU , KACPRZYK JANUSZ
Published: August 2007

The fuzzy set applications in political science cover decision making, games, collective choice, representation and comparative politics. The earliest applications were largely theoretical and suggestive rather than empirically anchored and testable models. We discuss a representative sample of applications and suggest some problems in making the fuzzy sets more generally applicable in political science.
ON ASYMPTOTICALLY λ-STATISTICAL EQUIVALENT SEQUENCES OF FUZZY NUMBERS
Authors: SAVAŞ EKREM
Published: August 2007

This paper presents the following definition which is a natural combination of the definitions for asymptotically equivalent and λ-statistical convergence of fuzzy numbers. The two sequences [X] and [Y] of fuzzy numbers are said to be asymptotically λ-statistical equivalent of multiple L provided that for every ∊ > 0 [Formula: see text] (denoted by [Formula: see text]) and simply asymptotically λ-statistical equivalent if L = 1. In addition, we shall also present asymptotically equivalent analogs of Savas's theorems in Ref. 7.