Wall Breach Research Articles

Physicochemical changes in sediments at Orplands Farm, Essex, UK following 8 years of managed realignment

Managed realignment (MR) is a ‘soft’ engineering technique that involves the deliberate landwards retreat of the existing line of coastal defence and subsequent tidal inundation of land. Managed realignment has been established worldwide for over 30 years and its goals may include habitat restoration, recovery of biodiversity and sustainable coastal defence. In southeast England in particular, an increasing number of MR sites (20–110 ha) have been commissioned in the last decade in response to increasing coastal habitat loss and sea-level rise. Following initial sea wall breaching and site flooding, monitoring of these sites is usually carried out for a period of 5 years and during this time changes in ecosystem structure can be easily observed. However, there is a poor understanding of the long-term effects of flooding on soil physicochemical parameters including sediment geochemistry and geochemical cycling, nutrient fluxes and soil maturation processes. Such physical and chemical changes may continue to take place over time-scales exceeding 5 years and therefore current monitoring practices may not be sufficient. This paper examines the changes in the physicochemical parameters of sediments in vertical core sections at the Orplands Farm MR site, Blackwater Estuary, Essex, 8 years after its flooding in 1995. Post-breach sediment accumulation rates at the site have been determined and a multi-proxy approach has been used to identify a pre-breach land surface. Soil development and the vertical distribution of saltmarsh plants following breaching have also been examined. The species saturation index approach has been used to provide an indication of the success of MR at this site. The pre-breach land surface was identified at 4–6 cm depth indicating a sediment accumulation rate ca. 0.75 cm a −1 since the site was breached in 1995. This sedimentation rate exceeds the regional sea-level rise of 0.1–0.3 cm a −1 and hence marsh development at the site is expected to continue in the short term. The examination of physicochemical parameters with depth indicates that the pre-breach land surface forms a barrier that may inhibit vertical tidal flushing, nutrient transfer and contaminant removal. The vegetation was mostly a pioneer and low-mid marsh assemblage typical of the area, although the species saturation index is low compared to other European sites and this may be attributed to a range of factors including poor drainage at the site and reduced seed availability.

Failure Mechanisms of Polymer-Reinforced Concrete Masonry Walls Subjected to Blast

Recent terrorist attacks indicate the improvised explosive device as the choice terror tactic. Over the past decade, the U.S. Department of Defense has encouraged and sponsored research toward developing methods of reinforcing structures to protect building occupants from the effects of external explosion. The focus of wall reinforcement research has recently shifted from applying stiff fiber-reinforced composites to using lower-strength higher-elongation elastomeric polymers that can be easily applied to the wall interior. This paper presents recent efforts that have demonstrated an innovative use of thin-membrane elastomeric polymers to prevent breaching and collapse of unreinforced masonry walls subjected to blast. The complex array of failure mechanisms observed from recent explosive tests is discussed. Effects of structural and nonstructural parameters are described with the aid of finite-element simulations. Finally, the needs and direction of future blast reinforcement developments are outlined.

Pedicle screw fixation strength: pullout versus insertional torque

Background context Researchers studying early pedicle screw designs have suggested that pullout strength and insertional torque are correlated. For surgeons using pedicle screws, insertional torque is widely believed to be a good predictor of pullout strength and initial stability of the screw and construct. How appropriate is this assumption when applied to new screw and thread designs? Purpose This study investigated the correlation between insertional torque and pullout strength of three different pedicle screw designs, with different insertional torque characteristics. We hypothesized that a significant increase in insertional torque would indicate a commensurate increase in pullout strength. Study design Biomechanical analysis of instrumented vertebral specimens. Methods Calf lumbar vertebra were prepared and instrumented with one of three pedicle screws. Pilot hole preparation was standardized and coaxial orientation was confirmed by direct inspection. Screws did not penetrate the pedicle cortex or abut or penetrate the anterior vertebral cortex. Any specimen with pedicle wall breach was discarded. The pedicles were instrumented with one of three screws: 1) 7.5×40 mm conical, asymmetric progressive thread (Xia; Stryker Spine, Allendale, NJ), 2) 7.5×40 mm conical with traditional V-shaped thread (Osteonics, Stryker Spine, Allendale, NJ)) or 3) 6.5×40 mm cylindrical with V thread (Osteonics, cylindrical). Paired testing allowed individual screws to be directly compared with a contralateral “control.” Insertional torque and peak torque values were recorded for each rotation up to full insertion. Pullout testing was conducted at a rate of 1 mm/minute. Load-displacement data were recorded at 20 Hz. Stiffness was considered the slope of the most linear part of the curve before the yield point. Results Peak loads for 7.5 conical Xia screws measured 1,783±589.1 N compared with 1,943.0±625.8 N for 7.5 conical Osteonics screws and 1,641.0±356.7 N for 6.5 cylindrical Osteonics screws. The peak insertional torque values were 6.7±1.9 Nm (158% greater than control), 4.5±1.1 Nm (73% greater than control) and 2.6±0.7 Nm, respectively. Insertional torques for Xia screws were significantly greater than conical (p=.001) and cylindrical Osteonics screws (p<.0001), and insertional torques for Osteonics conical screws were significantly greater than those of cylindrical screws (p<.0001). Although pullout loads for the conical Osteonics screws were consistently higher than either the Xia or Osteonics cylindrical screws, the differences were not significant (p>.05). There was no significant correlation between pullout strength and insertional torque (p>.05). Conclusions This unexpected result is best explained by the progressively narrowing flutes of the Xia screw, which compact the trabeculae into a smaller volume as the screw nears full insertion. The trapezoidal threads also increase contact with the cortical surface area and compress trabeculae toward the cortex, thus creating greater friction and higher torque values. This increase in torque did not translate into a commensurate increase in pullout strength, where trabeculae fail in shear.

Rapid morphological changes at the summit of an active volcano: reappraisal of the poorly documented 1964 eruption of Mount Etna (Italy)

While the eruptive record of Mount Etna is reasonably complete for the past 400 years, the activity of the early and late 1960s, which took place at the summit, is poorly documented in the scientific literature. From 1955 to 1971, the Central and Northeast Craters were the sites of long-lived mild Strombolian and effusive activity, and numerous brief episodes of vigorous eruptive activity, which led to repeated overflows of lava onto the external flanks of the volcano. A reconstruction of the sequence of the more important of these events based on research in largely obscure and nearly inaccessible sources permits a better understanding of the eruption dynamics and rough estimates of erupted volumes and of the changes to the morphology of the summit area. During the first half of 1964, the activity culminated in a series of highly dynamic events at the Central Crater including the opening of a fissure on the E flank of the central summit cone, lava fountains, voluminous tephra emission, prolonged strong activity with continuous lava overflows, and growth of large pyroclastic intracrater cones. Among the most notable processes during this eruption was the breaching of a section of the crater wall, which was caused by lateral pressure of lava ponding within the crater. Comparison with the apparently similar summit activity of 1999 allows us to state that (a) lava overflows from large pit craters at the summit are often accompanied by breaching of the crater walls, which represents a significant hazard to nearby observers, and that (b) eruptive activity in 1999 was much more complex and voluminous than in 1964. For 1960s standards however, the 1964 activity was the most important summit eruption in terms of intensity and output rates for about 100 years, causing profound changes to the summit morphology and obliterating definitively the former Central Crater.

Solid phase partitioning of metals in managed retreat soils: field changes over the first year of tidal inundation

Sequential extraction methods were used to determine the effect of saline inundation on partitioning behaviour of metals in soils at Orplands Managed Retreat site, Essex, UK. A suite of metals (Al, Ca, Cr, Cu, Fe, K, Li, Mn, Ni, Pb and Zn) were analysed in sequential extracts from samples of soil cores extracted immediately before breaching of sea walls in 1995 and 1 year after. Generally, partitioning of most metals was dominated by associations with the residual fraction and an absence of associations with the exchangeable fraction indicating a relatively uncontaminated environment. Changes in partitioning were predominantly limited to the top 8 cm of the soil profile where a decaying mat of vegetation from the pre-inundation surface resulted in high moisture contents and low redox potentials. In this zone, the predominance of metal associations with the residual fraction was replaced by associations with more labile fractions. In the surface layer deposited after breaching, Ca was dominantly associated with the carbonate fraction, which indicates biogenic import from adjacent estuarine sediments.

Phase transition behavior of a linear macromolecule threading a membrane

The problem of a polymer molecule whose two ends reside on opposite sides of a membrane or partition separating two solutions is solved exactly in the limit of no self-excluded volume. The monomers can go from one side of the membrane to the other only by threading serially through one hole in the membrane. The ends can be free, confined to run freely on the membrane surfaces, or be fixed to specific points on the membrane. It is found that the equilibrium thermodynamic phase transition is first order in all cases so that slight changes in pH, ionic strength, or temperature can move the polymer from being completely on one side of the membrane to being completely on the other side. Application to two biological problems are suggested: (1) the breaching of cell walls by the nuclear material of T2 bacteriophages, and (2) the transport of drugs that are affixed to these translocating polymers. The relation of this newly discovered transition to four other phase transitions that occur in isolated macromolecules (helix–random coil; equilibrium polymerization; polymer collapse; surface adsorption) is briefly discussed.

Differentiation and cell wall degrading enzymes in the obligately biotrophic rust fungus Uromyces viciae-fabae

Rust fungi differentiate a series of complex infection structures to infect their host plants. Artificial membranes providing a signal for the induction of infection structure differentiation have been used to study events taking place during early stages of host–pathogen interaction. During the prepenetration phase, serine esterases, one of which shows cutinase activity, appear to be important for adhesion of uredospores of Uromyces viciae-fabae to the plant cuticle. When the fungus grows through the stomatal opening, chitin deacetylase activity increases drastically. The role of this enzyme in masking and preventing degradation of fungal structures by plant chitinases is discussed. Different isoforms of protease, cellulase, and pectin methylesterases (PME) are formed when the fungus enters the intercellular space, and synthesis of polygalacturonate lyase (PL) coincides with formation of haustorial mother cells. Based on the physicochemical and catalytic properties of these cell wall degrading enzymes a model is presented that explains highly localized breaching of plant cell walls by obligate biotrophs. cDNAs corresponding to genes activated during late stages of infection structure differentiation of Uromyces viciae-fabae have been isolated by differential hybridization. The transcripts of the genes designated rif16 and rif21 occur when haustorial mother cells are formed, and the corresponding gene products may thus be important for successful infection. Key words: adhesion, cell wall degrading enzymes, chitin deacetylase, infection structure differentiation, penetration process, rif genes.

Cytological studies of early stages of powdery mildew in barley and wheat. IV. Direct ingress from superficial primary germ tubes and appressoria of Erysiphe graminis hordei on barley leavest

Breaching of barley leaf epidermal walls from superficial primary germ tubes and appressoria of Erysiphe graminis hordei on barley leaves was examined by micromanipulation within a scanning electron microscope. At 2 h after inoculation, penetration pegs, approximately 0·6 μm in diameter, were first observed on the contact surfaces of some primary germ tubes. Concurrently, penetration pores of 0·4 to 0·6 tsm diameter were observed in tracks of the same primary germ tubes on the cuticular surfaces. Similar penetration pores were also first visible below appressoria 6 h or more after inoculation. By 4 h after inoculation, epidermal walls were breached and papillae were induced by nearly 71 % of primary germ tubes; by 8 h, nearly 91 %. By 6 h after inoculation, host walls were breached and papillae were induced by about 5% of appressoria and by 18 h, 84%. By 8 h after inoculation, host walls were breached from both primary germ tubes and appressoria which had emerged from the same conidia. These results suggest that primary germ tubes of E. graminis hordei make physiological contact with host cells before appressorial penetration.

The Unmetamorphosed Sedimentary Fill of the Brent Meteorite Crater, Southeastern Ontario

A 10 000-ft (~3050-m) diameter circular structure that exhibits rimmed crater form, shock-metamorphic features, and underlying unbrecciated basement rocks occurs near Brent, Ontario, close to the southern margin of the Canadian Shield. In its center 863 ft (263 m) of Middle Ordovician sediments are preserved. Shortly after impact a nearly level crater floor was established and the subsequent sequence appears to have been deposited close to mean sea level. Repeated sediment laminae probably reflected wind-tidal marine incursions onto the low relief margin of the contemporary Ordovician epicontinental sea. Throughout much of its period of sediment accumulation, the crater floor appears to have been nearly flat. A 380-ft (115.8 m) sequence of dolostones, arkosic siltstones, and evaporite layers and veins formed within a breccia-rimmed depression. Initially sea water carrying fine silt invaded the crater and refluxed through the porous and permeable crater rim. Subsequently some 100 ft (30.5 m) of silty arkose blanketed the area, probably resulting from further transgression of the Middle Ordovician seas and breaching of the crater walls. An upper 380 ft (115.8 m) of predominantly thin-bedded lagoonal and shallow shelf sea limestones are divided into upper and lower sequences by a middle regressive set of red beds.The implied near-flat crater floor, coupled with preservation of over 800 ft (&gt;244 m) of crater sediments, suggests continued slow subsidence. Earlier on, this subsidence affected only the crater area, but later episodes of subsidence were regional, involving Ordovician, Silurian, and Devonian sedimentation. The superincumbent load further compacted the total crater sequence. Preservation of the rocks described here is due to final depression of the sequence into a position below the general level of the surrounding Precambrian terrain. If Brent can be considered to be a typical peri-marine meteoritic impact crater, all such craters should have in common an inward-dipping succession of open-circulation sediments overlying a crater-rim restricted sedimentary sequence, which in turn overlies a shock-metamorphosed series of breccias.Compaction of the impact-generated breccias and subsequent unmetamorphosed crater-filling sediments influenced both sediment accumulation and the ultimate crater structure.