Individual Domes Research Articles

Structural evolution of the North Himalaya domes as revealed by crustal-scale seismic-reflection surveying

As the typical products of collisional orogeny, gneiss domes are important geological units with which to decipher the crustal deformation and evolutionary history of continental collision. However, their formation mechanisms remain poorly understood. This issue is well illustrated by the debate surrounding the origin of the North Himalaya gneiss dome zone, which has been attributed to middle-crustal channel flow, thrust-duplex development, extensional detachment faulting, or diapiric flow related to partial crustal melting. These models predict different internal structures within individual domes that can be tested by high-resolution seismic imaging. Here, we present newly acquired seismic-reflection data collected along an ∼120-km-long north-south traverse across the central segment of the North Himalaya gneiss dome zone. Analysis and interpretation of the seismic data constrained by surface geology observations imply that (1) the subducting Indian lower crust is decoupled from the deformed middle and upper crust in the North Himalaya, (2) a crustal-scale stack of antiformal duplexes with a structural thickness of ∼35 km defines the cores of the gneiss domes imaged by the seismic survey, and (3) highly reflective, sheetlike bodies imaged in our seismic profile are best interpreted as leucocratic intrusions developed synchronously during gneiss dome development. As a whole, our work suggests that the North Himalaya gneiss dome zone was created by coeval crustal shortening and partial melting of orogenic crust.

Domes and semi-capsules as model systems for infrared microspectroscopy of biological cells

It is well known that infrared microscopy of micrometer sized samples suffers from strong scattering distortions, attributed to Mie scattering. The state-of-the-art preprocessing technique for modelling and removing Mie scattering features from infrared absorbance spectra of biological samples is built on a meta model for perfect spheres. However, non-spherical cell shapes are the norm rather than the exception, and it is therefore highly relevant to evaluate the validity of this preprocessing technique for deformed spherical systems. Addressing these cases, we investigate both numerically and experimentally the absorbance spectra of 3D-printed individual domes, rows of up to five domes, two domes with varying distance, and semi-capsules of varying lengths as model systems of deformed individual cells and small cell clusters. We find that coupling effects between individual domes are small, corroborating previous related literature results for spheres. Further, we point out and illustrate with examples that, while optical reciprocity guarantees the same extinction efficiency for top vs. bottom illumination, a scatterer’s internal field may be vastly different in these two situations. Finally, we demonstrate that the ME-EMSC model for preprocessing infrared spectra from spherical biological systems is valid also for deformed spherical systems.

Characteristics and consequences of lava dome collapse at Ruawahia, Taupo Volcanic Zone, New Zealand

The eruption of large, rhyolitic lava domes may be accompanied by the formation of large block and ash flows. This may be linked to the style of dome extrusion—whether it forms a series of individual lobes, flows or spines (exogenous) or grows by internal inflation (endogenous). Lava domes can transition from one extrusive style to another as a result of a change in extrusion rate or the formation of facilitating structures such as shear zones. How this change can affect large rhyolitic lava domes is unclear as there are few historically recorded rhyolitic dome eruptions. Here, we present structures at Ruawahia lava dome (a well exposed ~ 700-year-old lava dome), how these facilitating structures enable exogenous extrusion at Ruawahia dome, and link this to collapse episodes along the fringes of the dome during growth. Ruawahia dome is part of the Tarawera dome complex, a chain of domes running parallel to regional structures across the Okataina caldera complex in the Taupo Volcanic Zone, New Zealand. Ruawahia dome consists of (1) a high porosity (44–52%), crystalline (65% DRE), locally brecciated carapace facies with rare bread-crusting and ‘ropey’ flow textures; (2) a core facies of dominantly low to moderate porosity (20–25%) with elongate vesicles that mark weak flow bands; and (3) thin (< 5 m thick) interior breccia zones. Flow bands at Ruawahia are complex and do not fit with hypothesised flow band orientations attributed to a single phase of exogenous or endogenous dome growth. Inward dipping flow bands on ramp structures on the flow surface suggest a flow-like (coulee) morphology; however, steeply dipping and multidirectional flow bands on the edges of the dome challenge this hypothesis. Widespread block and ash flow deposits have been sourced from the leading dome fronts to the NW and SE; these collapse events left behind inflated and bread-crusted outcrops on these dome fronts, suggesting syn-eruption collapse events that led to expansion of a hot, pressurised dome interior. We consider Ruawahia erupted from multiple, aligned vents, either as lobes confined within the crater of a pyroclastic cone formed during the initial Plinian phase of the eruption or those able to flow down the cone flank. The confined lobes formed steep internal breccia zones as individual dome lobes extruded past one another. Lobes that were able to overcome the pyroclastic cone rim (or where the vent was outside the crater) were able to flow down the flanks as bulldozing, thickening flows with dominantly ductile interiors and brittle exteriors; these flows collapsed as the front thickened, possibly due to a decrease in gradient, producing widespread block and ash flows. The removal of lava associated with collapse generated a decompression event which resulted in fragmentation, cracking and vesiculation in the hot interior of the lava flows. These events left behind a re-vesiculated and bread-crusted lava flow front and produced block and ash flows with abundant breadcrust bombs that reached the base of Tarawera.

Physiological significance of gravity receptors on larval cephalic cuticle in the silk moth, Antheraea proylei Jolly.

The lateral aspects of larval cephalic cuticle of oak tasar moth, Antheraea proylei, a hybrid between Antheraea pernyi and Antheraea roylei exhibited the presence of gravity receptors in the form of dorsal campaniform sensilla. The distribution pattern and number of dome shaped dorsal campaniform sensilla were found to vary in different larval stages. In the first and second larval stages, 4-5 sensilla were localized near the apex of the lateral aspects of the cephalic cuticle on either side of the head. From the third larval stage onwards, on the other hand, both the right and left lateral aspects of the cephalic cuticle were covered with innumerable dome shaped dorsal campaniform sensilla. The sensilla were found to be arranged in groups of 3 to 5 on the cephalic cuticle with dome-free cuticular portion of about 50-100 µm in length between two adjacent groups of the sensilla. The individual dome shaped dorsal campaniform sensillum was either smooth surfaced or was covered with smaller domes through out the surface. The significance of differences in the number and distribution pattern of the dorsal campaniform sensilla among different larval stages in relation to gravity reception and preferred feeding posture are discussed in the light of available literature.

Evolution of tuff ring-dome complex: the case study of Cerro Pinto, eastern Trans-Mexican Volcanic Belt

Cerro Pinto is a Pleistocene rhyolite tuff ring-dome complex located in the eastern Trans-Mexican Volcanic Belt. The complex is composed of four tuff rings and four domes that were emplaced in three eruptive stages marked by changes in vent location and eruptive character. During Stage I, vent clearing produced a 1.5-km-diameter tuff ring that was then followed by emplacement of two domes of approximately 0.2 km3 each. With no apparent hiatus in activity, Stage II began with the explosive formation of a tuff ring ~2 km in diameter adjacent to and north of the earlier ring. Subsequent Stage II eruptions produced two smaller tuff rings within the northern tuff ring as well as a small dome that was mostly destroyed by explosions during its growth. Stage III involved the emplacement of a 0.04 km3 dome within the southern tuff ring. Cerro Pinto’s eruptive history includes sequences that follow simple rhyolite-dome models, in which a pyroclastic phase is followed immediately by effusive dome emplacement. Some aspects of the eruption, however, such as the explosive reactivation of the system and explosive dome destruction, are more complex. These events are commonly associated with polygenetic structures, such as stratovolcanoes or calderas, in which multiple pulses of magma initiate reactivation. A comparison of major and trace element geochemistry with nearby Pleistocene silicic centers does not show indication of any co-genetic relationship, suggesting that Cerro Pinto was produced by a small, isolated magma chamber. The compositional variation of the erupted material at Cerro Pinto is minimal, suggesting that there were not multiple pulses of magma responsible for the complex behavior of the volcano and that the volcanic system was formed in a short time period. The variety of eruptive style observed at Cerro Pinto reflects the influence of quickly exhaustible water sources on a short-lived eruption. The rising magma encountered small amounts of groundwater that initiated eruption phases. Once a critical magma:water ratio was exceeded, the eruptions became dry and sub-plinian to plinian. The primary characteristic of Cerro Pinto is the predominance of fall deposits, suggesting that the level at which rising magma encountered water was deep enough to allow substantial fragmentation after the water source was exhausted. Isolated rhyolite domes are rare and are not currently viewed as prominent volcanic hazards, but the evolution of Cerro Pinto demonstrates that individual domes may have complex cycles, and such complexity must be taken into account when making hazard risk assessments.

An Inexpensive Weight Bearing Indicator With Load Range Capability for Rehabilitation of Patients With Lower Extremity Injuries

This paper investigates the mechanical behavior and design of a patent pending device called a load range weight bearing indicator (LWBI), which provides upper and lower range indication to patients with lower extremity injuries as part of a partial weight bearing rehabilitation. The LWBI consists of two opposing stacks (a.k.a. double stack) of snap domes—bistable mechanical elements that snap through only when a threshold weight is applied—sandwiched between a load transfer plate and base plate. The mechanical behavior of a LWBI has been characterized by testing single and double stacks of snap domes in a rigid aluminum fixture using a universal testing machine. Single stacks of two to eight snap domes each exhibited very predictable and repeatable buckling behavior (i.e., stack buckling load is simply the sum of individual snap dome buckling loads) when deflected at speeds typical for patients walking with a regular gait. The double stack configuration only works when supporting legs of the opposing snap dome stacks are offset by half the angle between adjacent legs. The lower load stack buckles first, while the higher load stack buckles at its threshold load because of the very low force required to keep the lower load stack collapsed. While the presence of a spacer has little effect on the double stack buckling behavior under controlled rate deflection in a precision test fixture, it was required for proper functioning of a LWBI prototype probably because of looser dimensional tolerances. The type of substrate that snap dome stacks are in contact with has little effect on the buckling loads as long as the material is not too soft. Finally, the speed of deflection within the expected range of ambulating patients has an insignificant effect on the LWBI’s buckling behavior. A LWBI prototype was designed based on the observed characteristics of the snap dome double stack with a spacer plate between the upper and lower load stacks. The prototype was installed in a recess in the insole of a biomechanical shoe beneath the patient’s heel. The shoe with LWBI was tested by various subjects pushing on a force plate and the upper and lower buckling loads were clearly indicated to the subject by audible and tactile click and measured as ground reaction force versus time. Future work will focus on further testing of the device and refinement of the design for various medical appliances.

Highlights of Archives of Facial Plastic Surgery

Archives of Facial Plastic SurgeryVol. 11, No. 3 Regular DepartmentsFree AccessHighlights of Archives of Facial Plastic SurgeryPublished Online:1 May 2009AboutSectionsPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail Facial Fractures in Motor Vehicle Collisions: Epidemiological Trends and RisksFacial trauma is the most common injury to occupants in motor vehicle collisions (MVCs). Using the National Automotive Sampling System Crashworthiness Data System database (1993-2005), Brian T. McMullin, MD, and colleagues determined that the incidence of facial fractures from MVCs is decreasing. Newer car models and seatbelt use with frontal airbags were associated with a decreased risk of facial fracture from MVCs, whereas airbags alone had no impact on facial fracture risk, and side collisions as well as significant vehicle crash size mismatch were associated with a significantly higher risk of facial fracture.See page 165Free Tissue Reconstruction Following Excision of Head and Neck Arteriovenous MalformationsArteriovenous malformations (AVMs) in the head and neck can be quite aggressive and destructive. Surgical excision is the mainstay of treatment in the head and neck and has the potential for creating large and complex defects. Local tissue is often preferred for reconstruction of these defects, but at times is not feasible. Larry D. Hartzell, MD, and colleagues describe a series of 8 patients who had extensive head and neck AVMs that were resected and reconstructed using free tissue transfer. They found that most patients' AVMs recurred and that revision procedures were frequently necessary to remove residual malformation and improve the overall wound healing process, but that free tissue transfer offers a reliable and successful method of reconstruction.See page 171Nitrogen Plasma Skin Regeneration and Aesthetic Facial Surgery: Multicenter Evaluation of Concurrent TreatmentConcurrent ablative skin resurfacing of areas of the face that have undergone surgical rejuvenation potentially creates significant risk of damage to the undermined tissue. Nitrogen plasma skin regeneration is non–chromophore dependent and involves the transduction of radio frequency energy to the skin surface using ionized nitrogen gas, resulting in predictable thermal damage to the skin without an open wound, and offers an alternative to traditional ablative laser method for facial resurfacing. J. David Holcomb, MD, and colleagues describe a series of 95 patients who underwent nitrogen skin plasma regeneration and facial rejuvenation surgery during a single operative setting. With a 1.8% overall rate of transient complication, they conclude that combining nitrogen plasma skin regeneration with aging face procedures is safe with improved outcomes compared with aging face surgery alone.See page 184Domal Stabilization Suture in Tip RhinoplastyNasal tip suture modification techniques provide reliable and reversible methods for controlling the nasal tip while maintaining nasal tip support mechanisms. Anthony Corrado, DO, and colleagues present the “dome stabilization suture” as another option for refining and securing the nasal tip. The dome stabilization suture is placed along the cephalic borders of the domes at the medial third of the lateral crura bilaterally, just posterior to the junction of the intermediate and lateral crura, as a final step of the tip rhinoplasty. The authors present their experience with 100 cases using this technique and conclude that it complements other nasal tip modification maneuvers, providing a predictable method to align and stabilize the individual dome segments without affecting nasal tip rotation or projection.See page 194Le Repos, by Édouard Manet (1832-1883).See page 216This issue's Highlights were written by Amit Bhrany, MD.FiguresReferencesRelatedDetails Volume 11Issue 3May 2009 InformationCopyright 2009 American Medical Association. All Rights Reserved. Applicable FARS/DFARS Restrictions Apply to Government Use.To cite this article:Highlights of Archives of Facial Plastic Surgery.Archives of Facial Plastic Surgery.May 2009.156-156.http://doi.org/10.1001/archfaci.2009.32Published in Volume: 11 Issue 3: May 1, 2009PDF download

Differentiation of Epithelial Na+ Channel Function: AN IN VITRO MODEL

Confluent monolayers of epithelial cells grown on nonporous support form fluid-filled hemicysts called domes, which reflect active ion transport across the epithelium. Clara-like H441 lung adenocarcinoma cells grown on glass supports and exposed to 50 nM dexamethasone developed domes in a time-dependent fashion. Uplifting of small groups of cells occurred within 6-12 h, well formed domes appeared between 24 and 48 h, and after 7 days, individual domes started to merge. Cells inside of domes compared with those outside domes, or with monolayers not exposed to dexamethasone, differed by higher surfactant production, an increased cytokeratin expression, and the localization of claudin-4 proteins to the plasma membrane. In patch clamp studies, amiloride-blockable sodium currents were detected exclusively in cells inside domes, whereas in cells outside of domes, sodium crossed the membrane through La3+-sensitive nonspecific cation channels. Cells grown on permeable support without dexamethasone expressed amiloride-sensitive currents only after tight electrical coupling was achieved (transepithelial electrical resistance (R(t)) > 1 kilohm). In real-time quantitative PCR experiments, the addition of dexamethasone increased the content of claudin-4, occludin, and Na+ channel gamma-subunit (gamma-ENaC) mRNAs by 1.34-, 1.32-, and 1.80-fold, respectively, after 1 h and was followed by an increase at 6 h in the content of mRNA of alpha- and beta-ENaC and of alpha1- and beta1-Na,K-ATPase. In the absence of dexamethasone, neither change in gene expression nor cell uplifting was observed. Our data suggest that during epithelial differentiation, coordinated expression of tight junction proteins precedes the development of vectorial transport of sodium, which in turn leads to the fluid accumulation in basolateral spaces that is responsible for dome formation.

Numerical modelling of tephra fallout associated with dome collapses and Vulcanian explosions: application to hazard assessment on Montserrat

Abstract Hazardous effects of tephra fallout on Montserrat include roof collapse, aviation threats, health hazards from respirable crystalline silica, crop pollution, road safety and lahar generation. An advection-diffusion model was developed to investigate tephra dispersal from dome collapses and Vulcanian explosions, which generated most of the fallout tephra during the 1995-1999 eruptive period of Soufrière Hills Volcano. Wind field, atmospheric diffusion, gravity settling, aggregation and elutriation processes are considered. Computed isomass maps compare well with field observations and require aggregation of fine ash for good agreement. Probability maps were also compiled. Individual probability maps (for individual dome collapses and Vulcanian explosions) are based on the statistics of wind profiles and show that fallout tephra generated by individual eruptive events on a Montserrat scale do not cause serious damage in any area on Montserrat. Cumulative probability maps (for a given scenario of activity) are generated by sampling statistical distributions of wind profiles and eruptive events over an extended period of time. They show that persistent tephra fallout can accumulate enough material to cause roof collapses and serious damage to vegetation in the SW part of the island, and minor damage to vegetation in the north, as also confirmed by field data.

Wallrock alteration in the Bendigo gold ore field, Victoria, Australia: Uses in exploration

The Bendigo goldfield, which has produced most of Victoria's gold (22 million ounces=684.3 ton), consists of numerous deposits located mainly along narrow, parallel-trending anticlinal domes separated by 100 to 400 m. The individual domes are parts of a regional anticlinorium in Lower Ordovician sedimentary rocks. Highest gold ore values are generally located in the eastern limbs and particularly in the apical areas of the smaller individual anticlinal domes and in the central part of the more regional-anticlinorium. Alteration present in metasandstone units in the Nell Gwynne anticline consists of phengitic sericite (to 15 vol%), chlorite (to 7%), carbonates (siderite, sideroplesite, ankerite and calcite, to 10%) and sulphides (arsenopyrite, pyrite, chalcopyrite and sphalerite, to 5%). The alteration generally follows the trend of the structure extending upward and above mineralisation in anticlinal areas and below largely unmineralised synclinal areas. Phengitic sericite extends furthest, to at least 150 m above mineralised saddle reef positions, chlorite to 130 m, sulphides to 80 m and carbonate to 50 m. Chlorite geothermometry suggests temperatures of 260 to 290°C for the alteration. The sequence of carbonate precipitation generally is from siderite (early), sideroplesite, ankerite and calcite. The more Fe-rich carbonates tend to occur near the apical parts of the anticlinal domes. Arsenopyrite occurs within 10 m of the veins, while hydrothermal pyrite, chalcopyrite and sphalerite all extend to 50 m. Framboidal pyrite (possibly greigite) present in unaltered metasediments becomes progressively recrystallised and replaced by hydrothermal pyrite, chalcopyrite and sphalerite as mineralisation is approached. Hydrothermal pyrite is generally euhedral and anomalous in having high As contents when compared to framboidal pyrite. Maximum Au grades (205 ppm) occur in the saddle reef position and below a thick shale unit. Lower-grade mineralisation (0.5–6.0 ppm) occurs above this in the overlying stratigraphy. As and Pb anomalies cross cut the alteration zoning and occur as plume-like dispersion haloes above the mineralisation. The Au occurs in and near the As `plume'. Cu concentrations reach their maximum values adjacent to high Au values. Measured CO 2 values confirm the observed carbonate distributions. H 2O + and Zn values in the section show relatively random distributions. Two separate stages of mineralisation are indicated, the earlier localised within classic saddle reef structures and containing the highest Au, Cu and some As and a later, cross-cutting stage of mineralisation associated with high As. The alteration is mainly associated with the former.

Dome growth and destruction during the 1989–1990 eruption of redoubt volcano

Much of the six-month-long 1989–1990 eruption of Redoubt Volcano consisted of a dome-growth and -destructive phase in which 14 short-lived viscous silicic andesite domes were emplaced and 13 subsequently destroyed. The life span of an individual dome ranged from 3 to 21 days and volumes are estimated at 1 × 10 6 to 30 × 10 6 m 3. Magma supply rates to the vent area averaged about 5 × 10 5 m 3 / day for most of the dome-building phase and ranged from a high of 2.2 × 10 6 m 3 per day initially to a low of 1.8 × 10 5 m 3 per day at the waning stages of the eruption. The total volume of all domes is estimated to be about 90 × 10 6 m 3 and may represent as much as 60–70% of the volume for the entire eruption. The site of 1989–1990 dome emplacement, like that in 1966, was on the margin of a north-facing amphitheatre-like summit crater. The domes were confined on the east and west by steep cliffs of pre-eruption cone-building volcanic rocks and thus were constrained to grow vertically. Rapid upward growth in a precarious site caused each dome to spread preferentially to the north, resulting in eventual gravitational collapse. As long as the present conduit remains active at Redoubt Volcano, any dome formed in a new eruption will be confined to a narrow steeply-sloping gorge, leading to rapid vertical growth and a tendency to collapse gravitationally. Repetitive cycles of dome formation and failure similar to those seen in 1989–1990 are probably the norm and must be considered in future hazard analyses of Redoubt Volcano.

Effect of nonuniform spectral dome transmittance on the accuracy of infrared radiation measurements using shielded pyrradiometers and pyrgeometers

We discuss the problem arising from the nonuniform distribution of spectral transmittance of the instrument's shielding dome. Recently, by using high-resolution atmospheric radiation software, itbecame possible to evaluate both the real downward IR spectral flux density and the transmitted spectral flux density of the instrument's dome. By using a simplified model we obtained a theoretical formula that describes the effect of dome transmittance on the instrument's response. By the formula, the effective dome transmittance (average dome transmittance weighted by the spectral flux density) is directly proportional to the calibration constant of the instrument. In order to obtain a quantitative relationship we computed the effective dome transmittance for several domes and model atmospheres. ccording to our results the maximum difference in effective dome transmittance of individual domes is 20% for Eppley-type silicon domes and 10% for polyethylene domes. These relatively large differencesmust be corrected when the domes are replaced. The effective dome transmittance shows strongcorrelation with precipitable water and the total downward IR flux density. The combined effect on thecalibration factor is a maximum 2% for the Eppley domes and 5% for the polyethylene domes. By usingthe linear regression method these types of error can be minimized.

Siliciclastic Stromatolites and Thrombolites, Late Miocene, S.E. Spain

ABSTRACT Large coarse-grained siliciclastic stromatolite and thrombolite domes, forming biostromes and bioherms, occur in a marine fan-delta environment of Messinian age in the Sorbas Basin, Spain. Individual domes are up to 3 m in height and have estimated synoptic relief up to 1.5 m. They occur on a shelf-to-basin transition in the Terminal Complex, a mixed siliciclastic-carbonate unit which grades from coarse conglomeratic fan-delta and oolite deposits on the shelf, to basinal sands and silts of the Sorbas Member. Paleoslopes up to 35 degrees, extending downward for several hundred of meters to original water-depths of 70 m or more, mark the transition to the basin. Normal marine conditions are indicated by coralline algae and Porites within the domes. Thrombolites are restricted to he shelf and upper slope and are closely associated with stromatolites. The domes of the mid-slope and deeper environments are exclusively stromatolitic. Medium to coarse siliciclastic sand is common in domes at all depths except on the inner shelf, where ooids are dominant. Quartz and metamorphic rock pebbles and granules are locally present in the thrombolites and stromatolites of the shelf-edge and upper slope, and boulders form nuclei of some of these domes. Carbonate grains, mainly ooids and peloids, are present in all domes. However, the dominant carbonate component is mainly micrite in the form of micro-bushes and clotted fabrics. Important controls in the formation of these siliciclastic stromatolites and thrombolites were: 1) supply of siliciclastic grains, and 2) early carbonate cementation to maintain the relief of the domes during formation and to preserve primary fabrics after burial. Depth-limited microbial components of the mats, probably algae, may have assisted in trapping coarse sediment. They were also possibly responsible for limitation of the thrombolites to the shallow shelf environment.

Oolite stromatolites and thrombolites, Miocene, Spain: analogues of Recent giant Bahamian examples

At El Joyazo in Almeria, southeast Spain, closely packed thrombolite and stromatolite domes of Messinian age form a bioherm 12 m thick surrounded by oolite. Individual domes, up to 1.5 m high and 4 m across, are typically composite, with distinct stromatolitic and thrombolitic parts which are sharply juxtaposed. Both parts are composed of ooid and peloid fine-medium sand. Stromatolitic parts show good lamination and often contain small finger-like columns. Thrombolite is more abundant than stromatolite and has a distinct clotted fabric produced by irregular fenestrae. In size, general shape, internal structure, depositional environment (ooid shoal), grain size (fine-medium sand), and grain composition (ooids, peloids) the stromatolitic parts of the domes are closely comparable with Recent “giant” subtidal columnar stromatolites at Lee Stocking Island, Bahamas, and we regard them as analogues of these Recent examples. At present no modern analogues are known for the thrombolites. Previously, large Messinian stromatolites elsewhere in southeast Spain have been attributed to hypersalinity caused by the Mediterranean “salinity crisis”. The El Joyazo examples formed in current-swept ooid shoal environment, probably of normal marine salinity. We suggest that mobile sands, rather than hypersaline conditions, provided the stress to inhibit predators and competitors. These “giant” Messinian coarse-grained domes, like the Lee Stocking Island stromatolites, may have formed because of the presence of algae, such as chlorophytes and diatoms, capable of trapping large grains.

Control of ion transport in the thyroid: prostaglandin E2 activates cation transport on the basal membrane of cultured porcine thyroid cell monolayers

Confluent monolayers of cultured porcine thyroid cells transport fluid from the apical to the basal surface, forming circumscribed zones of detachment (domes) from the culture dish substrate. Stimulation of fluid transport by prostaglandin E2 (PGE2; 1 mumol/l) was associated with an increase in transepithelial potential (TEP). Intracellular potentials (equal to the potential difference across the apical membrane of the cell, Eapical) and the TEP were measured in individual domes so that the potential difference across the basal membrane of the cell (Ebasal) could be calculated from the relationship TEP = Eapical-Ebasal. The PGE2-induced increase in TEP was associated with hyperpolarization of the basal membrane, accompanied by a slight depolarization of the apical membrane. Lines of best fit by least-squares regression showed Eapical = -20.3 mV +0.219 TEP (correlation coefficient r = 0.627; P less than 0.001) and Ebasal = -20.3 mV -0.781 TEP (r = 0.944; P less than 0.001). Phenamil (1 mumol/l), a Na+ channel selective amiloride analogue, reduced the TEP from 13.25 +/- 0.58 (S.E.M.; n = 56) to 2.39 +/- 0.16 mV (n = 51; P less than 0.001) and hyperpolarized the apical membrane potential from -20.7 +/- 0.68 (n = 60) to -32.2 +/- 0.83 mV (n = 105; P less than 0.001). The response of the TEP to phenamil was immediate, and was promptly reversed on washing; in contrast, addition of 5-(N-ethyl-N-isopropyl)amiloride (20 mumol/l; selective for Na+/H+ antiporters) resulted in a slow depolarization over 30 min with a slow recovery after washout.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural tests of diapir hypotheses in Archean crust of Ontario

Detailed structural maps of two granitoid complexes in the Wabigoon Subprovince are used to test three diapir hypotheses advanced in earlier papers. The gneiss masses of, and individual domes within, the complexes fail the test for solid-state diapirism. The gneiss domes also fail the test for tensile bending caused by hypothetical magmatic diapirs in the subsurface. An oval pluton located near the best-exposed gneiss dome proves to be a synformal sheet rather than a funnel-shaped magmatic diapir. This pluton could be a syenite–diorite phacolith emplaced into a concordant zone of dilation during the late upright folding of the gneiss mass about horizontal axes. Earlier tight folds were probably recumbent and south verging and, like the gneissosity, generated in a ductile shear regime with subhorizontal glide planes. These observations have important implications for Archean tectonics, especially the relative horizontal displacement of large greenstone masses (potentially allochthonous greenstone belts).

Effects of exposure to NO 2 on dome formation in alveolar epithelial cell monolayers

Primary cultured monolayers of rat Type II pneumocytes were used to investigate the effects of NO2 on alveolar epithelial barrier properties. Such monlayers form fluid-filled domes which are thought to result from active solute transport from medium to substratum, with water following passively. Using dome formation as a transport marker, 5-day-old cultures were directly exposed to 30 ppm NO2 in 5% CO2/air at 25 degrees C by cyclically tilting culture plates from side to side such that both halves of the monolayer were exposed during each cycle. Exposures consisted of 10 cycles of 4 min each (2 min per side), for a cell exposure time of 20 min. Control plates were simultaneously exposed to 5% CO2/air under identical conditions. Twenty-four hours after exposure, NO2-exposed monolayers exhibited significant decreases in dome density and individual dome volume as compared to controls. By 48 hr postexposure, differences between NO2-exposed and control values were less but remained significant. Control monolayers were essentially unaffected by exposure to 5% CO2/air. These results show that short-term sublethal exposures to NO2 produce a decrease in dome formation in Type II alveolar epithelial cell monolayers. This finding is most likely due to a decrease in the active transepithelial sodium transport rate and/or an increase in the permeability of cell membranes or tight junctions.

On tight junction structure: Forssman glycolipid does not flow between MDCK cells in an intact epithelial monolayer

One model of tight junction structure suggests that lipids might flow from cell to cell within shared exoplasmic membrane leaflets. We tested this proposal by co-culturing two clones of MDCK epithelial cells, which differed in their content of Forssman glycolipid, and then staining by immunofluorescence with rabbit anti-Forssman Ig. In co-cultures grown on glass cover slips and on nitrocellulose filters, positive Forssman staining was restricted to sharply demarcated clusters of cells formed by the Forssman-positive clone. Integrity of tight junctions between the two clones was indicated on cover slips by the presence of individual domes (hemicysts) composed of both clones and on filters by the generation of transepithelial potential differences. These results suggest that glycolipids in the exoplasmic leaflet of cells in a tight epithelium do not flow to adjacent cells.

Electrical currents flow out of domes formed by cultured epithelial cells.

Domes are localized areas of fluid accumulation between a cultured epithelial cell monolayer and the impermeable substratum on which the cells are cultured in vitro. Dome formation has been documented in a variety of epithelial cell lines that retain their transepithelial transport properties in vitro. However, it is not known whether domes are predominantly areas of specific active transport, or, alternatively, are predominantly areas of relative weak attachment to the culture surface. In the present study we adapted a vibrating microelectrode, which can detect small currents flowing in extracellular fluid, to determine if current was flowing into or out of domes and thereby to determine if domes were specialized areas of active transport. We used alveolar type II cells as the main epithelial cell type because they readily form domes in vitro and because they transport sodium from the apical to the basal surface. We found that electrical current flowed out of domes. The direction of the current was independent of the size of a dome, of the age of an individual dome, and of the number of days in primary culture for alveolar epithelial cells. This current was inhibited by amiloride and ouabain and was dependent on sodium in the medium. We made similar observations (outward current from domes which is blocked by amiloride and by sodium substitution) with domes formed by the Madin-Darby canine kidney cell line. The data support the hypothesis that sodium is transported across the entire monolayer and leaks back mainly through the domes. We conclude that domes in epithelial monolayers are not predominantly special sites of active transport but are more likely simply areas of weak attachment to the substratum.

Dome formation in primary cultured monolayers of alveolar epithelial cells.

We have observed the formation of domes by type II alveolar epithelial cells harvested from rat lungs. The cells were harvested using elastase and grew to confluence in 3-4 days after plating on plastic. Numerous domes were observed in the monolayers 4-18 days after plating, with peak dome density occurring at days 6-9. When trypsin was used instead of elastase as the harvesting enzyme, many fewer domes were formed by the monolayers, with peak dome density observed at day 5 and no domes seen after 8 days. The life span of an individual dome was about 3-4 h. The presence of domes indicates an intact active transport function of the cells in the monolayer, which may represent an important mechanism for the maintenance of fluid-free air spaces and normal alveolar fluid balance in mammalian lungs in vivo.