The (U–Th)/He method has been applied to constrain the formation ages of the Clearwater West and East impact structures of Quebec, Canada. Zircons were separated from impact melt samples derived from ...a surface exposure at Clearwater West (32 km diameter), and from a drill core at Clearwater East (26 km diameter). The (U–Th)/He results indicate ages of 280±27 Ma (2σ, n=7) for Clearwater West, and 450±56 Ma (2σ, n=8) for Clearwater East. Our (U–Th)/He date for Clearwater West supports the findings of previous Rb–Sr (266±15 Ma; 2σ) and 40Ar/39Ar (280±4 Ma and 283.8±2.2 Ma, 2σ) impact melt studies. Our (U–Th)/He date for Clearwater East also overlaps with previously published 40Ar/39Ar dating results, which yielded U-shaped spectra, with ‘maximum’ and ‘best-estimate’ dates of ∼ 460–470 Ma. Our results support the contention, previously based solely on 40Ar/39Ar data, that the Clearwater West and East impact structures do not comprise an impact doublet that formed coevally from a binary asteroid pair.
•We dated the Clearwater Lake impact craters (Canada) via the (U–Th)/He zircon method.•Results presented here indicate that the adjacent twin craters formed ∼170 Ma apart.•Suggesting Clearwater East and West impact craters do not comprise an impact doublet.
The resistant ~50 m thick Vera Rubin ridge (VRR) situated near the base of Mount Sharp, Gale crater, Mars, has been deemed a high priority science target for the Mars Science Laboratory mission. This ...is because of (1) its position at the base of the 5 km layered strata of Mount Sharp and (2) the detection of hematite from orbit, indicating that it could be the site of enhanced oxidation. The compositional data acquired by the Alpha Particle X‐ray Spectrometer (APXS) during Curiosity's exploration of VRR help to elucidate questions pertaining to the formation of the ridge. APXS analyses indicate that VRR falls within the compositional range of underlying lacustrine mudstones, consistent with a continuation of that depositional environment and derivation from a similar provenance. Lower Fe concentrations for VRR compared to the underlying strata discounts the addition of large amounts of hematite to the strata, either as cement or as detrital input. Compositional trends are associated with VRR cross‐cut stratigraphy, indicating postdepositional processes. Higher Si and Al and lower Ti, Fe, and Mn than the underlying mudstone, particularly within distinct patches of gray/blue bedrock, are consistent with the addition of Si and Al. Lateral and vertical compositional variations suggest enhanced element mobility and fluid flow (possibly via multiple events) through VRR, increasing toward the top of the ridge, consistent with the action of warm (~50–100°C), locally acidic saline fluids as inferred from the mineralogy of drilled samples.
Plain Language Summary
Curiosity has explored the resistant Vera Rubin ridge (VRR) at the base of Mount Sharp, Gale crater, Mars, owing to (1) its position within the 5 km layered rocks of Mount Sharp, which record changes in Mars environment through time, and (2) the detection of hematite from orbit. The Alpha Particle X‐ray Spectrometer (APXS) measures the elemental composition of rocks. APXS analyses indicate that VRR has a similar composition to underlying mudstones, consistent with continued deposition in a lake. Lower iron discounts the addition of large amounts of hematite, holding together mineral grains either as cement or as detrital grains. Other elemental trends cut across layering, indicating postdepositional processes. Lateral and vertical compositional variations suggest enhanced element mobility and fluid flow (possibly via multiple events) through VRR, particularly at the top of the ridge and within gray/blue patches of bedrock, consistent with the action of warm (~50–100°C), acidic saline fluids inferred from the mineralogy of drilled samples.
Key Points
Vera Rubin ridge is compositionally a continuation of the Murray formation
Compositional trends cut across stratigraphy, are postdepositional, diagenetic, and/or products of later alteration
APXS data indicate enhanced fluid flow and Si, Al, and Mn mobilization within VRR
Alpha Particle X‐ray Spectrometer (APXS) results for Phase 2 of the Bagnold Dunes campaign, focusing on the linear dunes, complement those from Phase 1 (barchan dunes) and add to our understanding of ...active Martian dune systems. This work highlights both compositional similarities and differences across the dune field. The concentration of elements associated with mafic minerals in coarser grains and along active ripple crests, previously identified in the barchan dunes, highlights differences in Martian and terrestrial weathering, transport, and sorting processes. Concentration of a Cr‐Ti mineral phase within the linear sands is identified. The inactive ripple fields are geochemically similar to soil, while active ripple fields are similar to sands. Inferred dust content (S + Cl + Zn concentrations), derived from APXS analyses, provide geochemical confirmation of current and seasonal activity variations, within the barchan and linear dunes, as well as revealing a continuum between inactive soils and active sands.
Plain Language Summary
During 2015–2017, the Mars Science Laboratory rover, Curiosity, in Gale Crater, Mars, crossed the active Bagnold Dunes, which comprise both barchan (crescent shaped) and linear dunes. This has enabled the first in situ appraisal of an active dune system on another planet, including the geochemical analysis (major elements, plus Ni, Zn, and Br) of sand samples via the Alpha Particle X‐ray Spectrometer. We find a concentration of elements (MgO and Ni) associated with mafic minerals (particularly olivine) along the crests of active ripples and in coarse‐grained samples. Elements such as SiO2, Al2O3, and K2O, associated with more felsic minerals such as plagioclase, are concentrated in off‐crest sand and finer‐grained portions. We find evidence for a Cr2O3‐TiO2 mineral phase, concentrated in the linear dunes. Dust content (indicated by SO3, Cl, and Zn levels) indicates that activity levels are higher in the linear dunes than in the barchan dunes.
Key Points
Alpha Particle X‐ray Spectrometer results reveal compositional similarity between basaltic Bagnold barchan and linear sands (Gale Crater)
Evidence of mineral segregation, and mafic element concentration in coarser fractions, along active ripple crests is observed
Linear sands show evidence for the concentration of a Cr‐Ti mineral phase, previously undetected in the barchan dunes
We present Alpha‐Particle X‐ray Spectrometer (APXS) data for the active Bagnold dune field within the Gale impact crater (Mars Science Laboratory (MSL) mission). We derive an APXS‐based average ...basaltic soil (ABS) composition for Mars based on past and recent data from the MSL and Mars Exploration Rover (MER) missions. This represents an update to the Taylor and McLennan (2009) average Martian soil and facilitates comparison across Martian data sets. The active Bagnold dune field is compositionally distinct from the ABS, with elevated Mg, Ni, and Fe, suggesting mafic mineral enrichment and uniformly low levels of S, Cl, and Zn, indicating only a minimal dust component. A relationship between decreasing grain size and increasing felsic content is revealed. The Bagnold sands possess the lowest S/Cl of all Martian unconsolidated materials. Gale soils exhibit relatively uniform major element compositions, similar to Meridiani Planum and Gusev Crater basaltic soils (MER missions). However, they show minor enrichments in K, Cr, Mn, and Fe, which may signify a local contribution. The lithified eolian Stimson Formation within the Gale impact crater is compositionally similar to the ABS and Bagnold sands, which provide a modern analogue for these ancient eolian deposits. Compilation of APXS‐derived soil data reveals a generally homogenous global composition for Martian soils but one that can be locally modified due to past or extant geologic processes that are limited in both space and time.
Key Points
Gale soils are compositionally similar to a global basaltic Martian soil but with slight evidence of local contribution
The sands of the Bagnold barchan dunes are compositionally distinct with mafic enrichment
The active Bagnold sands are low in dust as evidenced by low S, Cl, and Zn concentrations
The Glen Torridon stratigraphic sequence marks the transition from the low energy lacustrine‐dominated Murray formation (Mf) (Jura member: Jm) to the more diverse Carolyn Shoemaker formation (CSf) ...(Knockfarril Hill member: Knockfarril Hill; Glasgow member: Glasgow). This transition defines a change in depositional setting. Alpha Particle X‐ray Spectrometer (APXS) results and statistical analysis reveal that the bulk primary geochemistry of Mf targets are broadly in family with CSf targets, but with subtle compositional and diagenetic trends with increasing elevation. APXS results reveal significant compositional differences between Jura_GT and the stratigraphically equivalent Jura on Vera Rubin ridge (Jura_VRR). The data define two geochemical facies (high‐K or high‐Mg), with a strong bimodal grain distribution in Jura_GT and Knockfarril Hill. The contact between Knockfarril Hill and Glasgow is marked by abrupt sedimentological changes but a similar composition for both. Away from the contact, the Knockfarril Hill and Glasgow plot discretely, suggesting a zone of common alteration at the transition and/or a gradual transition in provenance with increasing elevation in the Glasgow member. APXS results point to a complex history of diagenesis within Glen Torridon, with increasing diagenesis close to the Basal Siccar Point unconformity on the Greenheugh pediment, and with proximity to the beginning of the clay sulfate transition. Elemental mobility is evident in localized enrichments or depletions in Ca, S, Mn, P, Zn, Ni. The highly altered Hutton interval, in contact with the unconformity on Tower butte, is also identified on Western Butte, indicating that the “interval” was once laterally extensive.
Plain Language Summary
The Mars Science Laboratory Curiosity rover has traversed the Glen Torridon locale in Gale crater, Mars. The rover has provided evidence in the rocks of a change from a lake setting to a river setting, with increasing elevation through the rock record. Geochemical results from the Alpha Particle X‐ray Spectrometer (APXS) confirm a slow change in composition over time as the sediments that formed the rock were laid down. Fluids percolated through the sediments, altering the composition, with localized enrichments of calcium, sulfur, manganese, phosphorus, sodium, zinc, nickel, which are now present as veins, and small (typically <0.3 cm; more rarely, 0.5–2 cm) rectangular nodules and concentrations.
Key Points
Alpha Particle X‐ray Spectrometer data for Glen Torridon, Gale crater documents subtle compositional changes
Multiple episodes of alteration and diagenesis identified
Compositional similarities between Glen Torridon members confirms the highly localized nature of the Vera Rubin ridge alteration
Chemical data acquired by Curiosity's Alpha Particle X‐ray Spectrometer during examination of the contact between the upper Mount Sharp group and overlying Stimson formation sandstones at the ...Greenheugh pediment reveal compositional similarities to rocks encountered earlier in the mission. Mount Sharp group strata encountered below the Basal Siccar Point group unconformity at the base and top of the section, separated by >300 m in elevation, have distinct and related compositions. This indicates enhanced post‐depositional fluid flow and alteration focused along this contact. Sandstone targets exposed immediately above the unconformity have basaltic compositions consistent with previously encountered eolian Stimson formation sandstones, except at the contact, where they show the addition of S. Resistant sandstone outcrops above the contact have higher K, Mn, and Na and lower Ni concentrations that primarily reflect changes in provenance. They are compositionally related to cap rock float blocks encountered as Curiosity climbed through the Mount Sharp group, and Bradbury group sandstone outcrops. The higher K, pediment sandstones are interpreted to have a similar provenance to some Bradbury group sandstones, further evidence for widespread, alkaline source rock within and/or in the vicinity of Gale crater. The Bradbury and Siccar Point groups may both be younger than the Mount Sharp group. Alternatively, an alkaline source area in and around Gale crater has been eroded by both water and wind at different times (both before and after deposition of the Mount Sharp group), during the evolution of the crater and its infill.
Plain Language Summary
Chemical data acquired by Curiosity's Alpha Particle X‐ray Spectrometer during examination of an important regional contact between two rock units in Gale crater, Mars, reveal relationships with other rocks encountered much earlier in the mission. These relationships provide evidence for erosion by wind and water of various composition source rocks. These include more typical Martian basaltic and more alkaline composition rocks (e.g., higher potassium and sodium). Distinct chemistry within rocks immediately underlying the contact, separated by more than 300 m in elevation, indicate enhanced fluid flow and alteration along the contact. These relationships provide important insights into regional and crater‐scale processes and evidence for the long‐lived role of water and aqueous alteration and hence, habitable environments at Gale.
Key Points
Enhanced post‐depositional fluid flow and alteration of the Mount Sharp group was focused at the Basal Siccar Point group unconformity
Alkaline source rocks at Gale provided detritus to fluvial and eolian sandstones
Bradbury and Siccar Point group sandstones may be contemporaneous, and younger than the Mount Sharp group
Objective We sought to evaluate exercise performance and quality of life in children after surgical repair of anomalous aortic origin of a coronary artery with an interarterial course. Methods ...Patients who had surgery from October 2001 to January 2007 were eligible for inclusion. Exercise performance and quality of life were prospectively assessed by maximal exercise tests and age-appropriate questionnaires, respectively. We used t tests to compare pre- and postoperative exercise data and quality-of-life scores to published normative data. We performed linear regression analyses to assess associations between demographic, anatomic, and exercise variables and quality-of-life score. Results Of 25/27 patients, 64% were boys, 68% had anomalous right coronary, 32% were asymptomatic. Average age at surgery was 10.8 (±4.1) years; median follow-up was 14.5 (2 to 48) months. Postoperative percent-predicted exercise values were: peak heart rate 97 (±6), working capacity 91 (±15), maximal oxygen consumption 82 (±16). In those who had preoperative exercise testing (n = 11), resting and maximal heart rates decreased significantly without significant change in exercise performance. Average child quality of life was 85/100 (±13) and parent-proxy 88 (±11) compared with normal scores of 83 (±15) and 88 (±12), respectively. Conclusion There is mild chronotropic impairment in children and adolescents following anomalous coronary artery repair without a decline in exercise performance. This does not appear to impair their overall quality of life. Because long-term effects on heart rate, exercise performance, and quality of life are unknown, serial exercise tests should be included as routine care of these patients.
The expression and functional properties of connexin36 (Cx36) were examined in two communication-deficient cell lines (N2A-neuroblastoma and PC-12 cells) transfected with Cx36 and in hippocampal ...neurons that express the connexin endogenously. Transfected cells expressed the expected 2.9 kb Cx36 transcript and Cx36 immunoreactivity, whereas nontransfected cells were devoid of Cx36. The relationship between steady-state junctional conductance (g(j)) and transjunctional voltage was well described by a two-state Boltzmann equation. The half-inactivation voltage (V(0)), the ratio of minimal to maximal g(j) (g(min)/g(max)), and the equivalent gating charge were +/- 75 mV, 0.55, and 1.75, respectively, indicating that Cx36 exhibits very low voltage sensitivity. Conductance of single Cx36 channels measured with patch pipettes containing 130 mM CsCl was 10-15 pS (n = 15 cell pairs); despite this low unitary conductance, Cx36 channels were permeable to the dye Lucifer yellow. Hippocampal neurons expressed Cx36 both in vivo and in culture. The electrophysiological properties of channels in cultured hippocampal neurons were similar to those of the channels expressed by the transfected cell lines, and the neuronal channels were similarly permeable to Lucifer yellow. The unique combination of weak voltage sensitivity, small unitary conductance, and permeation by anions as large as second messenger molecules endows Cx36 gap junction channels with properties well suited for mediating flexible electrical and biochemical interactions between neurons.
Adenovirus infection in the lung results in graft failure after lung transplantation Bridges, Nancy D.; Spray, Thomas L.; Collins, Margaret H. ...
Journal of thoracic and cardiovascular surgery/The Journal of thoracic and cardiovascular surgery/The journal of thoracic and cardiovascular surgery,
10/1998, Volume:
116, Issue:
4
Journal Article
Peer reviewed
Open access
Objectives: Our goal was to examine the relationship between viral pneumonia and outcome in pediatric patients undergoing lung or heart-lung transplantation.
Methods: Prospective surveillance for ...common respiratory viruses of childhood was performed in all patients undergoing lung or heart-lung transplantation. Specimens were examined for the presence of replicating virus (by culture), viral genome (by polymerase chain reaction), and viral antigen (by immunofluorescence and immunohistochemical staining). The relationship between viral infection and outcome was examined.
Results: Sixteen patients underwent 19 transplants during the study period, with follow-up of 1 to 26 months. Virus was identified in the transplanted lung in 29 instances; adenovirus was identified most commonly (8/16 patients) and had the greatest impact on outcome. In 2 patients with early, fulminant infection, adenovirus was also identified in the donor. Adenovirus was significantly associated with respiratory failure leading to death or graft loss and with the histologic diagnosis of obliterative bronchiolitis (
P ≤ .002 in each case).
Conclusions: Adenovirus infection in the transplanted lung is significantly associated with graft failure, histologic obliterative bronchiolitis, and death. Health care personnel and families must be vigilant in preventing exposure of transplant recipients to this virus. Availability of a rapid and reliable test for adenovirus in donors and recipients would have an impact on management and could improve outcome for pediatric lung recipients. (J Thorac Cardiovasc Surg 1998;116:617-23)
Hepatocytes are well coupled by gap junctions, which allow the diffusion of small molecules between cells. Although gap junctions in many tissues are permeable to molecules larger than cAMP and in ...several preparations gap junctions pass cAMP itself, little direct evidence supports permeation by other second-messenger species. Ca2+, perhaps the smallest second messenger, would be expected to cross gap junctions, but the issue is complicated because gap-junction channels are closed when intracellular free Ca2+concentration, Ca2+i, is elevated to micromolar levels or above. Inositol 1,4,5-trisphosphate (InsP3), a second messenger that can evoke Ca2+release, might also reduce junctional permeability by this mechanism. We report here evidence for transjunctional flux of Ca2+and InsP3in freshly isolated pairs or small clusters of rat hepatocytes. The Ca2+indicator fura-2 was used to monitor transjunctional diffusion of Ca2+directly or to detect passage of InsP3by localized Ca2+release. Fura-2 injected as the free acid passed between cells. Injection of InsP3or CaCl2immediately increased Ca2+iin the injected cell (peak values < 1 μ M), and Ca2+iincreased rapidly in contacting cells (within seconds). The initial rise in Ca2+iinduced by InsP3was greater at discrete regions in the cytoplasm of both injected and uninjected cells and was inconsistent with simple diffusion of Ca2+. In the coupled cells the regions of greatest increase were not necessarily near the contact zone. In contrast, the rise induced in Ca2+iby CaCl2injection when cells were bathed in normal Ca2+was always more diffuse than with InsP3injection, and in cells coupled to a cell injected with CaCl2the earliest and maximal increases occurred at the region of cell contact. This difference in distribution indicates that injected InsP3(or an active metabolite, but not Ca2+) diffused between cells to cause localized release of Ca2+from intracellular stores. Ca2+injection induced a rise in Ca2+iin coupled cells even when cells were maintained in Ca2+-free saline, suggesting that changes in Ca2+iseen in adjacent cells were due to transjunctional diffusion from the injected cell and not to uptake from the extracellular solution. However, in Ca2+-free saline, Ca2+idistribution was nonuniform, indicating that Ca2+- releasing mechanisms contribute to the observed changes. No increase in Ca2+iwas seen in adjacent cells when Ca2+was injected after treatment with the uncoupling agent octanol (500 μ M), which itself did not change Ca2+i. These data provide evidence that the second messengers Ca2+and InsP3can be transmitted from cell to cell through gap junctions, a process that may have an important role in tissue function.
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