Narrow Fissures Research Articles

Spreading of tracer plumes through confined telogenetic karst aquifers: A model

Summary To calculate spreading of a tracer or contaminant through an aquifer all details of the aquifer, e.g. distribution of hydraulic parameters, must be known. This is not possible in nature. To study the spreading of plumes through karst, we have used a digital model of a confined karst aquifer at different stages of early karstification. In these models all details such as fracture aperture widths, their lengths and widths, and the hydraulic boundary conditions are known. Therefore the flow velocity of water can be calculated in each fracture. Using this information a particle tracking method is employed to calculate the propagation and spreading of a plume caused by an instantaneous input pulse into selected regions of the aquifer. From this information the time dependence of the outflow of particles from any selected region is obtained. This function represents the transfer response function for an instantaneous Dirac δ-function input. Two digital karst models are designed. In the first, homogeneous one, the aperture widths of the fractures are statistically distributed but of similar width. In the second a coarse percolating net of prominent fractures with larger constant aperture width is embedded into the dense net of narrow fissures. Propagation of the plumes and the transfer-response function are presented at the onset of karstification and at different times of karst evolution. If particles are injected at the entrance of evolving karst channels propagating towards the output boundary tracer breakthrough times increase with increasing time of karst evolution until shortly before breakthrough of the karst conduit they drop to half of their maximal value. With increasing evolution of the karst aquifer the hydraulic heads are redistributed and regions of low hydraulic gradients in the upstream side of the aquifer are created. Particles injected into fractures which have stopped dissolutional widening of their aperture widths and are located in regions of low gradient are kept in these regions for long times in the order of 100 years until they have propagated towards regions of high hydraulic heads, where a “fan like” plume develops along the pathway of steepest gradient.

The ecological relationships and demography of restricted ironstone endemic plant species: implications for conservation

We investigated the ecological relationships, reproductive biology and demography of four shrub taxa restricted to ironstone ranges in south-western Australia, to assess the feasibility of post-mining reintroductions. We found that three taxa were restricted to narrow fissures in massive ironstone and the fourth was restricted to fissures and skeletal soils over ironstone. In all taxa, adult plants were the most abundant life stage in populations and produced seeds annually. Newly emerged seedlings were observed in low numbers each winter of three census years, with the highest rates occurring when winter rainfall was above average in the semiarid Mediterranean climate. Mortality was highest and most variable for <1-year-old seedlings (50–93%), 1-year-old seedlings (17–67%), juveniles (21–54%) and vegetative adults (6–50%), and was lowest and least variable for the reproductive adults (2–7%). The restriction of three of our study taxa to narrow fissures excludes the option of using seedlings in reintroductions. Using seeds, although possible, will be both an inefficient and a high-risk strategy for at least three of the four taxa studied. This is because of the low frequency of years when winter rainfall is sufficient to stimulate high rates of seed germination, coupled with the consistently high rates of seedling mortality in most years, and no easy method for determining which rock fissures will be suitable for plant establishment. The more widespread taxa showed reproductive and demographic characteristics similar to those of the taxa restricted to the narrow fissures, indicating that establishment of many species will be difficult in this environment.

Highlights in DD

“Highlights” calls attention to exciting advances in developmental biology that have recently been reported in Developmental Dynamics. Development is a broad field encompassing many important areas. To reflect this fact, the section spotlights significant discoveries that occur across the entire spectrum of developmental events and problems: from new experimental approaches, to novel interpretations of results, to noteworthy findings utilizing different developmental organisms. Dissecting Down syndrome models (Embryonic and Not Maternal Trisomy Causes Developmental Attenuation in the Ts65Dn Mouse Model for Down Syndrome by Joshua D. Blazek, Cherie N. Billingsley, Abby Newbauer, and Randall J. Roper, Dev Dyn 239:1645–1653) Proper data interpretation is dependent upon a thorough understanding of experimental tools. The most widely used model for Down syndrome, or trisomy 21, is the Ts65Dn mouse. In an effort to determine the etiology of DS phenotypes, the authors discover that Ts65Dn embryos have attenuated development and are smaller than control embryos. The authors show that developmental attenuation is a consequence of embryonic trisomy. However, they find that another phenotype, a smaller than expected ratio of trisomic offspring at birth that further decreases at weaning stages, is influenced by the maternal genetic background. At embryonic stages, the small ratio is a product of maternal trisomy—Ts65Dn offspring are bred from Ts65Dn mothers. While at postnatal day 10, the decreased ratio may be due to a commonly found Pde6brd/rd maternal background mutation, which causes blindness in Ts65Dn mothers and possibly renders them less able to care for their young. The analysis highlights the importance of understanding the possible contributions of the maternal genetic background of the disease model during the analysis of embryonic and early postnatal phenotypes. Future studies will benefit from careful consideration of all underlying genetic contributions to phenotypes associated with disease models and diseased humans. Initial invasion (Cellular Dynamics of Epithelial Clefting During Branching Morphogenesis of the Mouse Submandibular Gland by Yuichi Kadoya and Shohei Yamashina, Dev Dyn 239:1739–1747) The mouse submandibular gland (SMG), a model for epithelial branching, starts out resembling a cauliflower with floret-like terminal clusters that are connected to an epithelial stalk. Over two days, the bulky primordia blossoms into a mature, many branched, tree-like organ. Epithelial branching starts with a cleft that dives into and carves apart terminal clusters. Here, Kadoya and Yamashima use live imaging of SMG cultures impregnated with a non-cell permeable fluorescent tracer, and transmission electron microscopy (TEM), and to identify characteristics of cleft formation. Clefts initially form when a narrow fissure extends between epithelial cells, but clefts are dynamic in that some retract, and the distal, invading end often changes direction before settling on a path of invasion. The latter finding suggests that cleft elongation must occur in the presence of epithelial cells with certain, unknown attributes. When a cleft invades between cells, the distal tip seemingly drives right into a cell making a small groove. At one side of the groove, this cell makes up the cleft sidewall, and at the other side the cell extends a small cytoplasmic projection that the authors call a shelf. Because the shelf harbors anchoring filaments, the authors suggest it might form an attachment to the basement membrane that covers the distal tip, generating a mechanical force that drives cleft extension. These careful observations call into question previous models of cleft elongation, and carve a path for future studies. Finding common ground (Molecular Haeckel by Richard P. Elinson and Lorren Kezmoh, Dev Dyn 239:1905–1918) In 1870, the German biologist and philosopher, Ernst Haeckel, authored a textbook that included his depiction of a 10-somite embryo with a caption that read, “embryo of a mammal or bird”. Although the inaccuracy of this and other similar figures outraged his fellow anatomists, in some ways, Haeckel was ahead of his time. In the 1980s, the field of evolutionary developmental biology (evo-devo) was born, based on the premise that diverse species share conserved gene regulatory networks that are tweaked throughout evolution to create morphological diversity. Incorporating concepts from evo-devo, Elinson and Kezmoh have updated Haeckel's concept of the “generic vertebrate embryo.” The authors conducted a thorough survey of the literature to identify regulatory genes whose expression in a specific tissue or organ was conserved across major vertebrate model systems. The information was transformed into pictoral form, where the names of the genes themselves are made into art and used to create the organs and tissues of a generic vertebrate embryo. The result is a set of drawings that are eye-catching, instructive, and most importantly, they are accurate. These are the first generation of so-called Molecular Haeckels; future versions could include additional criteria such as gene function.

Optimal Configuration of Hydrogen-Embrittlement-Fabricated Nanogaps for Surface-Conduction Electron-Emitter Display

Application of nanogaps for electron sources is fascinating in surface-conduction electron-emitter display. In contrast to rather complicated fabrication processes of the focused ion beam technique for the extremely narrow fissure, nanogaps fabricated by hydrogen embrittlement (HE) have thus been proposed as novel surface-conduction electron emitters due to their low turn-on voltage, high emission current, high focus capability, and high emission efficiency. In this paper, we theoretically investigate effects of the separation width and the tilted angle of the nanogaps fabricated by HE method on the field emission efficiency using a 3-D finite-difference time-domain particle-in-cell simulation technique. The structure with a large tilted angle may result in a high emitted current, but the collected current on the anode is suppressed due to the strong local field around the tip. A small structure prevents the emitted electrons from spreading out, and thus, no current could be collected by the anode. Also, the structure with a wide (or a narrow) separation of gap weakens (or enhances) the field around the tip and reduces the collected electrons. For better emission efficiency and focus capability, the separation width and the tilted angle of the examined structure could vary from 57 to 117 nm and 30deg to 60deg, respectively.

Oil in the lake of world heritage

Lake Baikal is the oldest and deepest lake in the world. It contains approximately 20% (23 · 10 3 km 3 ) of the world’s surface reserves. Since the community of diverse endemic organisms of the lake has not suffered from human impact at its recent stage of development [1], it is included into the UNESCO world heritage list. Unique features of Lake Baikal include natural oil seeps in its shelf zone, which have been known since the 18th century [2]. At oil shows in the middle and south sections of Lake Baikal, oil occurs as bitumen in shore cliffs or rises from the lake bottom as floating spherules of viscous hydrocarbons that make up spills (up to 1.5 m across) in an area of approximately 1 km 2 in summer. In winter, the floating oil is accumulated under ice as bituminous films and inclusions in narrow fissures. The oil composition corresponds to the biodegraded type. Its origin and age were debatable until recently [3]. In 2005, a new natural oil occurrence was discovered in deep-water settings of Lake Baikal that differs from the previously known ones. The discovery poses a problem concerning the role of natural oil occurrences in the ecosystem of the unique basin and its petroleum potential. The new oil occurrence was discovered in Middle Baikal (Cape Gorevoi Utes) owing to satellite observations of a dark spot (~1km across) on the lake surface in the spring of 2003. Observations of 2004 and 2005 showed that such a spot appears in this area every spring. In July 2005, numerous oil spots (up to 1 m in diameter) were recorded on the lake surface in an area of approximately 1 km 2 . Echo sounding revealed an underwater acoustic anomaly in the form of a gas flare ~500 m high. The oil sampled from the lake surface was studied using the gas chromatography/mass spectrometry method (Fig. 1). The samples contained n- alkanes, acyclic isoprenides, and polycyclic aromatic hydrocarbons. Based on the database including characteristics of molecular indicators for 76 genetically different oil fields [4], the ratios of molecular indicators (pristane/phytane 6.7; dibenzothiophene/phenathrene <0/1), and the low sulfur content (<0.08%), we concluded that the samples correspond to oils formed in sediments of deep freshwater basins during the Oligocene‐Early Miocene. This age estimate obtained for the Baikal oil based on molecular indicators is consistent with one hypothesis, according to which the Baikal oil is not older than the Cretaceous and it originates from organic matter buried in a freshwater basin [5]. The bottom sediments were sampled at the center of the gas flare and at its periphery (at a distance of 200 m). The core taken in the central part (0‐40 cm) is composed of dark gray reduced massive clayey‐silty sediment. The Holocene diatomaceous ooze layer typical of Baikal is missing at the surface. The sediment was mixed with oil and saturated with gas. The oil content exceeds 10% of the dry sediment. The second core demonstrates distinct bedding along its entire length. According to biostratigraphic data ( Cyclotella minuta, Aulacoseira baicalensis , and others), the sediment represents the Holocene diatomaceous ooze. The surface sediment (upper 4 cm with a brown color) is oxidized, while the remainder of the core is reduced (gray in color). The interval of 10‐40 cm hosts lenses and interbeds of silt and fine- to medium-grained sand with small brown oil droplets (up to 3 mm across) fringed by small gas bubbles. The oil content in this core interval is approximately 1% of dry sediment. The difference between two sampled cores in terms of oil-and-gas occurrence and lithology is probably explained by different intensities of their influx. The central part of the gas flare is characterized by permanent fluxes of gas, oil, and groundwater, which provide

Experimental study on water-oil migration and accumulation in a 2D micro-model of carbonate fracture media

Many achievements have been made in experimental studies of hydrocarbon migration in the clastic reservoir. On the other hand, few migration experiments have been reported in the carbonate reservoir simulation realm. This article is a tentative experimental study on hydrocarbon migration and accumulation in the carbonate reservoir, which is a complex media that includes a pore system and fracture system. This microcosmic experiment simulates oil-water displacement using a real core model. Plentiful seepage phenomena were observed in the microcosmic experiments. Three kinds of pathways were found in the plane: parallel pathway, oblique-cross pathway and network pathway. Three types of flow were found: continuous flow, sectioning flow and their combination. Three driving fronts were found in the experiment: piston front, encircle front and impulse front. All these vary with many factors such as fluid pressure, oil saturation, fissure configuration and wettability, and these factors affect each other. The results show that the relation between the fluid pressure and volume of flow is a complex segmenting correlation, instead of a simple positive correlation like the pipe flow that follows Darcy’s law. The relation between fluid pressure and the speed of flow also follows the same correlation. Speed of flow relates to the angle and width of the fissure. Speed of flow in the wide fissure that has an acute angle with the pressure gradient is faster than that in a narrow fissure with a high angle with the pressure gradient.

Nanometric Dispersion of a Mg/Al Layered Double Hydroxide into a Chemically Modified Polycaprolactone

Polycaprolactone (PCL) was chemically modified by grafting maleic anhydride on it, through a radical reaction induced by benzoyl peroxide as initiator. To improve the grafting degree, a second unsaturated comonomer such as glycidyl methacrylate (GMA) has been added, demonstrating a good reactivity in melt grafting without leading to long grafted chains. The quantitative determination of grafted maleic anhydride, performed by FTIR analysis, revealed a grafting weight percentage of 9.5 +/- 0.9, and the NMR characterization made it possible to propose a structure for the grafted polymer (PCLgMA). The modified polymer was analyzed by DSC and X-ray diffraction, showing a structural organization even better than that of the pristine polymer. An exchange reaction with a layered double hydroxide (LDH), hydrotalcite-like solid in the nitrate form, led to the disappearance of the crystalline basal peak of LDH in the X-ray diffractograms, suggesting a possible exfoliation of the inorganic sample. An oxidative etching on the composite surface followed by atomic force microscopy analysis made it possible to enlighten the lamellar structure in the pristine sample. In the composite sample, the well identifiable narrow fissures homogeneously distributed on the surface demonstrate that nanometer stacks of LDH sheets, embedded in a highly textured PCLgMA matrix, are present in the composite sample. The comparison of X-ray diffractograms and AFM analysis suggests either a partial exfoliation or an intercalation of the polymer in a lamellar texture with a basal spacing higher than 5 nm. In any case, the process of ionic exchange between nitrate LDH and PCLgMA led to the formation of nanocomposites, in which no large hydrotalcite aggregates are present. This is an interesting method to obtain a direct intercalation of the modified polymer into the inorganic solid with a simple ionic exchange reaction.

TU‐C‐330A‐03: Sulci Density Map to Aid in the Use of Apparent Diffusion Coefficient for Therapy Evaluation

Purpose: To quantify the density and spatial variation of sulci in the human brain so as to more accurately calculate Apparent Diffusion Coefficients (ADCs) for use in radiotherapy evaluation. Methods and Materials: ADCs are calculated for Volumes Of Interest (VOI) using Diffusion Weighted Magnetic Resonance Imaging (DWMRI).In the brain, the sulci are the narrow fissures separating convolutions and are filled with CerbroSpinal Fluid (CSF). Since CSF is free fluid, a VOI that contains a high density of sulci should, in principal, have a higher ADC.Using ImageJ (http://rsb.info.nih.gov/ij/), we have analyzed sagittal T1 weighted MR images of a number of patients. The images sets were acquired on one of two different GE MRI machines: 1.5T and 3.0T field strength. We have plotted the normalized pixel standard deviation, as a function of distance from a medial point. We have concentrated on the cerebral hemispheres, superior to the corpus callosum so as to focus on sulci and avoid voxel dissimilarities due to variations in other brain anatomy. Results: Relative to the 25% most medial slices, we see a decrease in the normalized standard deviation of pixel intensity of 13.7% ± 5.6% (SD) of the next 25% of the slices. The most lateral 50% of the slices (25% left and right) had about the same normalized standard deviation as the most medial (increase of 1.0% ± 7.1% (SD)). These results are consistent with the fact that near the periphery of each brain hemisphere, there are more sulci. Conclusion: Sulci density, as measured by normalized standard deviation of pixel intensity, has a substantial variation across the hemispheres of the brain. This fact should be considered when assessing variations in ADCs used for radiotherapy evaluation.

Anthropometric Comparison of Portraits of Korean and Japanese Beauty in the Late 18th and Early 19th Centuries

The aim of this study is to elaborate comparative portraits of Korean and Japanese beauty in the late 18th and early 19th centuries. Six portraits of beauty in the Korean Joseon Dynasty (early 19th century) and 5 in Japanese Edo Dynasty (late 18th century) were analyzed. Twenty anthropometric items were applied to the measure of the features on each portrait and 18 proportional indices of the face were calculated. Among the 18 indices, Korean and Japanese beauty did not show any significant differences in 13, but in 5: 1) the ratio of eye fissure to intercanthal distance was greater in Japanese beauty; 2) eye inclination was greater in Japanese beauty; 3) the ratio of nasal width to intercanthal distance was greater in Japanese beauty; 4) the ratio of nasal and facial width was greater in Korean beauty; and 5) the ratio of vermilion size to mouth width was greater in Japanese beauty. It is assumed that Korean had narrower eye fissure, lower eye inclination, wider nasal ala, and thinner lip than what Japanese craved during that era.

Foraging and roosting ecology of a rare insectivorous bat species, Laephotis wintoni (Thomas, 1901), Vespertilionidae

Laephotis wintoni is a rare bat and little is known about its biology. We studied this species at Algeria Forestry Station in the Western Cape Province, South Africa. A female caught in November 2002 was pregnant and three females caught in November 2004 were all lactating. The three lactating females were radio tagged and roosted in crevices or narrow fissures in a cliff face above the valley where they foraged. Laephotis wintoni is a small insectivorous bat (body mass, x̄ ± SD = 9.6 ± 0.5 g, n = 4) with low wing loading (7.0 ± 0.7 Nm−2, n = 4), low aspect ratio (5.7 ± 0.5, n = 4), low wingtip shape index (1.2 ± 0.2, n = 4) and long ears (20.9 ± 2.3 mm, n = 2). Its morphology suggests that it is a slow manoeuvrable flyer that can fly close to vegetation, or the ground or over water surfaces. Its relatively pointed wings suggest that it probably does not fly in dense clutter. Furthermore, it combines this wing shape with echolocation calls of relatively low intensity, short duration (2.6 ± 0.8 ms, n = 5), narrow band (13.5 ± 2.9 kHz, n = 5) and surprisingly low peak frequency (22.1 ± 0.6 kHz, n = 5). The latter two parameters make it unlikely that the calls are used to overcome masking effects associated with flying in dense clutter. Instead, we propose that its echolocation calls are adapted to be less audible to tympanate insects. This is supported by the fact its diet is dominated by moths in a habitat where tympanate moths comprise 90% of the moth population.

Flow field properties local to near-wall shear layers in a low Reynolds number turbulent boundary layer

Combined hot-wire anemometry and flow visualizations are used to explore the properties of near-wall shear layers in a low Reynolds number turbulent boundary layer (Rθ=U∞θ/ν≅1200). The experiments employed two four-element probes positioned in the buffer layer. Data from these sensors were acquired synchronously with high speed, dual view, 35 mm movies of vaporized mineral oil fog illuminated via two orthogonal laser sheets. Near-wall shear layers were identified as satisfying the visual criterion of a narrow fissure of passive marker moving upward through the buffer layer in concert with a strong deceleration in the axial velocity trace. The present results reveal that the local flow fields satisfying these criteria regularly contain adjacent and spatially compact regions of opposing-sign spanwise vorticity ωz in the streamwise/wall-normal plane. A number of features were identified relative to whether ωz at the upper probe was positive or negative. In this regard, the configuration with positive ωz located above a region of negative ωz correlated with a more rapid wall-normal transport of the passive marker. Conditionally averaged measurements indicate that the flows local to near-wall shear layers have an attenuated opposing effect relative to the long time vωz contribution to the Reynolds stress gradient. Overall, these observations point to the change-of-scale mechanism rather than gradient transport in establishing the large Reynolds stress gradient in the buffer layer. Both spatial configurations of ωz were revealed to have association with an advective acceleration upstream of the detected shear layer. The scale of this accelerated region was larger for the condition of negative ωz located above a region of positive ωz. The detection of near-wall shear layers had a strong visual correlation with clusters of spanwise vortices, often occurring in counter-rotating pairs.

Early karstification in a dual-fracture aquifer: the role of exchange flow between prominent fractures and a dense net of fissures

The early evolution of flow and hydraulic conductivity in a dual-fracture karst aquifer is investigated by numerical modelling. The initial aquifer consists of a dense net of narrow fissures with aperture widths a 0 and a coarser network of prominent fractures with aperture width A 0> a 0 embedded into it. Dissolutional widening by carbon dioxide containing waters aggressive to calcite increases hydraulic conductivity in the net and in the prominent fractures. To elucidate the effects of hydraulic and chemical coupling between these two flow systems the evolution of the karst aquifer has been modelled under constant head boundary conditions for various coupling strengths given by the ratio a 0/ A 0= M. For an isolated net of prominent fractures, a 0=0, and M=0 a conduit evolves along one of the percolating pathways and exhibits the well known breakthrough behaviour of single 1D conduits. With increasing coupling, M<0.3, the breakthrough times rise from 30 ky ( M=0) to 60 ky ( M=0.3), but the pattern of the fracture widening remains almost unchanged. With further increasing M the breakthrough times drop significantly and remain constant at values of about 4 ky for M>0.5. In these cases, owing to increasing a 0, short cuts through the narrow fissures become more favourable than breakthrough along the meandering pathway of the prominent fractures. It is shown that exchange flow between the prominent fractures and the dense net of narrow fissures plays an important role in the evolution of the aquifer. Flow from prominent fractures into the net can either leave the aquifer through this net, or it can return back into a pathway of prominent fractures downstream. In the first case enhanced inflow of aggressive solution into the prominent fractures at the input increases the dissolution rates and reduces breakthrough time consequently. In the other case the solution which reenters into a prominent fracture has gained a calcium concentration closer to equilibrium than that in the prominent fracture. This reduces dissolution rates in its downstream part an retards karstification. Our model scenarios presented show a complex interplay between these two mechanisms.

Shrapnell's membrane in a mammal exposed to extreme pressure variations: morphological and radiological observations in the hooded seal.

The function of Shrapnell's membrane (pars flaccida; PF) in middle-ear mechanics is still an enigma, though numerous proposals have been put forward, e.g. protection of pars tensa, equalizing of middle-ear pressure, sound transmission, and the site of origin of otitis media. In this study the PF was studied in a mammal (the hooded seal) which exposes itself to extreme pressure differences (from 1 to 100 atmospheres) when diving. Formaldehyde-fixed temporal bones obtained from newborn, one-year-old, and adult seals (three of each) were cleansed and decalcified in 10 per cent EDTA. The lateral wall of the middle-ear cavity, including the whole tympanic membrane with its bony surroundings, was then excised and photodocumented. Thin sections were cut parallel with, and perpendicular to, the handle of the malleus, stained with haematoxylin-eosin, toluidine blue or Giemsa stain and examined under a light microscope. One seal head was subjected to high resolution computerized tomography (HRCT) before sectioning. The PF was observed to be a narrow fissure measuring a maximum of 0.8 mm between processus brevis of the malleus and the notch of Rivinus in pars squamosa (pars tensa diameter 10-12 mm). It seems unlikely that the PF of the hooded seal participates in pressure equalization in the middle ear. The main function of the lateral wall of the attic, including the minimal PF, appears to be to protect the middle-ear ossicles and allow movement of the malleus.

Dam sites in soluble rocks: a model of increasing leakage by dissolutional widening of fractures beneath a dam

Water flowing through narrow fissures and fractures in soluble rock, e.g. limestone and gypsum, widens these by chemical dissolution. This process, called karstification, sculptures subterranean river systems which drain most of their catchment. Close to dam sites, unnaturally high hydraulic gradients are present to drive the water impounded in the reservoir downstream through fractures reaching below the dam. Under such conditions, the natural process of karstification is accelerated to such an extent that high leakage rates may arise, which endanger the operation of the hydraulic structure. Model simulations of karstification below dams by coupling equations of dissolutional widening to hydrodynamic flow are presented. The model scenario is a dam 100 m wide in limestone or gypsum. The modelling domain is a two-dimensional slice 1 m wide directed perpendicular to the dam. It extends 375 m vertically and 750 m horizontally. The dam is located in its center. This domain is divided by fractures and fissures into blocks of 7.5×7.5×1 m. The average aperture width of the fractures is 0.02 cm. We performed model runs on standard scenarios for a dam site in limestone with the height H of impounded water 150 m, a horizontal impermeable apron of width W=262 m and a grouting curtain reaching down to a depth of G=97 m. In a second scenario, we changed these construction features to G=187 m and W=82 m. To calculate widening of the fractures, well-established experimental data on the dissolution of limestone and gypsum have been used as they occur in such geochemical settings. All model runs show similar characteristic behaviour. Shortly after filling, the reservoir exhibits a small leakage of about 0.01 m 3 s −1, which increases steadily until a breakthrough event occurs after several decades with an abrupt increase of leakage to about 1 m 3 s −1 within the short time of a few years. Then, flow in the fractures becomes turbulent and the leakage increases to 10 m 3 s −1 in a further time span of about 10 years. The widths of the fractures are visualized in various time steps. Small channels propagate downstream and leakage rises slowly until the first channel reaches the surface downstream. Then breakthrough occurs, the laminar flow changes to turbulent and a dense net of fractures which carry flow is established. We performed a sensitivity analysis on the dependence of breakthrough times on various parameters, determining breakthrough. These are the height of impounded water H, the depth G of grouting, the average aperture width a 0 of the fractures and the chemical parameters, which are c eq the equilibrium concentration of Ca with respect to calcite and the Ca-concentration c in of the inflowing water. The results show that the most critical parameter is a 0. At fracture aperture widths of 0.01 cm, breakthrough times are above 500 years. For values of a 0>0.02 cm, however, breakthrough times are within the lifetime of the structure. We have also modelled dam sites in gypsum, which exhibit similar breakthrough times. However, after breakthrough, owing to the much larger dissolution rates of gypsum, the time until unbearable leakage is obtained, is only a few years. The modelling can be applied to complex geological settings, as phreatic cave conduits below the dam, or a complex stratigraphy with varying properties of the rock with respect to hydraulic conductivity and solubility. A few examples are given. In conclusion, our results support the assumption that increasing leakage of dam sites may be caused by dissolutional widening of fractures.

Exhalative Mineralization in Devonian Reef Complexes of theCanning Basin, Western Australia

Lenticular stromatolite-barite-sulfide mounds, interpreted as sedimentary exhalative deposits, are exposed at several localities in Devonian reef complexes of the Canning basin, Western Australia. These mounds, hundreds of meters long and tens of meters thick, occur along contacts between basinal shales (Gogo Formation) and marginal-slope limestones (Sadler Limestone) and adjacent to synsedimentary faults cutting the Gogo Formation. The mounds are limestone buildups, composed of stromatolites intergrown with barite and cut by iron sulfide veins. The iron sulfides (marcasite and pyrite) are weathered to gossans at the surface. They fill fissures that probably formed as a result of contemporary seismic activity and the early compaction of underlying and adjoining shales. The stromatolite-barite-sulfide deposits also occur as allochthonous clasts in penecontemporaneous debris-flow deposits. Postdepositional compaction of basinal shales in the Gogo Formation commonly amounted to about 75 percent. This resulted in the expulsion of large volumes of fluids along permeable interbeds, shale-limestone contacts, and synsedimentary faults, reaching the sea floor as cool-fluid seepages. The expelled fluids carried dissolved carbonate, barium, iron, and reduced sulfur. They probably nourished chemosynthetic bacteria that mediated the deposition of stromatolites, barite, and iron sulfides, resulting in growth of the stromatolite-barite-sulfide buildups. There is no known economic mineralization in the exhalative buildups, but some drill holes encountered minor uneconomic veins of epigenetic Zn-Pb mineralization, filling narrow fissures that postdate the exhalative deposits. Economic epigenetic Zn-Pb deposits that have been mined elsewhere in the same general area of the Canning basin were formed during the early Carboniferous or latest Devonian, many millions of years after the exhalative deposits. Both exhalative and epigenetic phases of mineralization are thought to have been sourced through the compaction-driven dewatering of shales. The exhalative deposits are interpreted to have formed over seepages of cool fluids having salinities close to that of seawater, whereas the epigenetic deposits formed from much hotter fluids, probably brines, expelled during subsequent shale compaction.

Solution structure of a mutant of transcription factor 1: implications for enhanced DNA binding

An NMR solution structure of a mutant of the homodimer protein transcription factor 1, TF1-G15/I32 (22 kDa), has been solved to atomic resolution, with 23 final structures that converge to an r.m.s.d. of 0.78 Å. The overall shape of TF1-G15/I32 remains similar to that of the wild-type protein and other type II DNA-binding proteins. Each monomer has two N-terminal α-helices separated by a short loop, followed by a three-stranded β-sheet, whose extension between the second and third β-strands forms an antiparallel β-ribbon arm, leading to a C-terminal third α-helix that is severely kinked in the middle. Close examination of the structure of TF1-G15/I32 reveals why it is more stable and binds DNA more tightly than does its wild-type counterpart. The dimeric core, consisting of the N-terminal helices and the β-sheets, is more tightly packed, and this might be responsible for its increased thermal stability. The DNA-binding domain, composed of the top face of the β-sheet, the β-ribbon arms and the C-terminal helices, is little changed from wild-type TF1. Rather, the enhancement in DNA affinity must be due almost exclusively to the creation of an additional DNA-binding site at the side of the dimer by changes affecting helices 1 and 2: helix 2 of TF1-G15/I32 is one residue longer than helix 2 of the wild-type protein, bends inward, and is both translationally and rotationally displaced relative to helix 1. This rearrangement creates a longer, narrower fissure between the V-shaped N-terminal helices and exposes additional positively charged surface at each side of the dimer.

Drilling and non-drilling predation in gastropod aggregations in the intertidal zone of a New Zealand Harbour

verge in scores on dead animal remains, and may also be active carnivores, thrusting the long proboscis through the narrow umbonal fissures of Chione and other bivalves”, as the universal scavenger of mud Members of the buccinid gastropod genus Cominella are abundant components of the intertidal fauna of many Australian and New Zealand sheltered beaches where they commonly form aggregations around food items1,2,3. For New Zealand, Morton & Miller2 desJ. Moll. Stud. (2000), 66, 419–422 © The Malacological Society of London 2000

A method for quantitatively estimating diffuse and discrete hydrothermal discharge

Submarine hydrothermal fluids discharge as undiluted, high-temperature jets and as diffuse, highly diluted, low-temperature percolation. Estimates of the relative contribution of each discharge type, which are important for the accurate determination of local and global hydrothermal budgets, are difficult to obtain directly. In this paper we describe a new method of using measurements of hydrothermal tracers such as Fe/Mn, Fe/heat, and Mn/heat in high-temperature fluids, low-temperature fluids, and the neutrally buoyant plume to deduce the relative contribution of each discharge type. We sampled vent fluids from the north Cleft vent field on the Juan de Fuca Ridge in 1988, 1989 and 1991, and plume samples every year from 1986 to 1991. The tracers were, on average, 3 to 90 times greater in high-temperature than in low-temperature fluids, with plume values intermediate. A mixing model calculates that high-temperature fluids contribute only ∼ 3% of the fluid mass flux but > 90% of the hydrothermal Fe and > 60% of the hydrothermal Mn to the overlying plume. Three years of extensive camera-CTD sled tows through the vent field show that diffuse venting is restricted to a narrow fissure zone extending for 18 km along the axial strike. Linear plume theory applied to the temperature plumes detected when the sled crossed this zone yields a maximum likelihood estimate for the diffuse heat flux of8.9 × 10 4 W/m, for a total flux of 534 MW, considering that diffuse venting is active along only one-third of the fissure system. For mean low- and high-temperature discharge of 25°C and 319°C, respectively, the discrete heat flux must be 266 MW to satisfy the mass flux partitioning. If the north Cleft vent field is globally representative, the assumption that high-temperature discharge dominates the mass flux in axial vent fields leads to an overestimation of the flux of many non-conservative hydrothermal species by about an order of magnitude.

Modultion of the Golgi apparatus in stimulated and nonstimulated prolactin cells of female rats

The three-dimensional structure of the Golgi apparatus and its compartments in prolactin cells has been examined in lactating rats in which secretion of prolactin was suppressed by removing the litter or stimulated by allowing the pups to suckle again. As soon as 2 hr after removal of the litter, large irregular progranules and numerous large pale vesicles accumulated in the trans-Golgi area together with vesicular or tubular fragments. The cis-tubular network was no longer recognizable on the cis-face of the Golgi ribbon; the saccules of the midcompartment were partitioned by narrow fissures and also became perforated in register by numerous fenestrations of various sizes and irregular contours. The concomitant appearance of numerous vesicles in the cavities thus formed as well as in the surrounding cytoplasm indicated that they probably arose by the progressive cavitation and fragmentation of saccules of the mid compartment. Such a process, which reached a maximum between 4 and 6 hr after removal of the litter from the mother, was no longer observed at 8 and 12 hr, at which time intervals the Golgi apparatus was reduced in size with no cis-tubular elements and progranules on its trans-aspect and few vesicles in its surroundings. When mothers, separated from their litters for a period of 12 hr, were returned to their pups for 20 min, the cis-tubular network reappeared on the cis-aspect of the Golgi stacks and presumably formed by fusion of vesicles and anastomosed tubules located next to the cisternae of the rough endoplasmic reticulum. In addition, the structure of the midsaccules returned to the stimulated condition, and early progranules were again segregated within the trans-most saccules of the Golgi stack. Hence, the Golgi apparatus of prolactin cells was rapidly and deeply modified in the presence or absence of stimulation.

Boxwork Fabric of Halloysite-Rich Kaolin Formed by Weathering of Anorthosite in the Sancheong Area, Korea

AbstractBoxwork fabric in which numerous thin or thick halloysite walls are interconnected into a microscopically porous cellular pattern is widely developed in the halloysite-rich kaolin formed by weathering of anorthosite in Sancheong, Korea. Studies using optical microscopy, scanning electron microscopy, and transmission electron microscopy have been carried out in order to elucidate the detailed features and origin of the boxwork.In the early stage of weathering, halloysite spheres formed in etch pits on the walls of microstructural discontinuities in the slightly weathered rock. With further weathering, the halloysite spheres grew to discs or flattened globules, which in turn coalesced to form large planar halloysite plates amid narrow fissures. The halloysite plates were detached by dissolution of the plagioclase in groundwater. Continued growth of the halloysite tubes in the plates resulted in the wrinkling of the plates. Finally, the plagioclase was completely dissolved by groundwater, leaving the boxwork of wrinkled halloysite walls and large pores. The relatively high rigidity of the boxwork is due to the compact agglomeration of halloysite tubes within the wrinkled halloysite walls.Cation balance calculation shows that Al was significantly mobilized during the formation of the boxwork in the weathering environment. The well-developed microfissures, the high dissolution rate of the calcic plagioclase, and the rapid flow of groundwater in a mountainous topography with relatively steep (20°) slope have been the factors controlling the formation of the porous boxwork in the halloysite-rich kaolin of the Sancheong area.