Terminal Proterozoic cyanobacterial blooms and phosphogenesis documented by the Doushantuo granular phosphorites II: Microbial diversity and C isotopes

An unprecedented period of phosphogenesis, along with massive deposition of black shales, major perturbations in the global carbon cycle and the rise of atmospheric oxygen, occurred in the terminal Proterozoic in the aftermath of the Marinoan glaciation. Although causal links between these processes have been postulated, evidence remains challenging. Correlated in situ micro-analyses of granular phosphorites from the Ediacaran Doushantuo Formation in Yichang, South China, suggested that cyanobacteria and associated extracellular polymeric substances (EPS) might have promoted aggregated granule growth and subsequent phosphatization (She et al., 2013). Here, we present new paleontological data for the Doushantuo phosphorites from Yichang, which, combined with Raman microspectroscopy and carbon isotope data, further document links between the biology of cyanobacteria and phosphogenesis. Mapping of microfossils in thin section shows that most phosphatic granules contain microfossils that are dominated by colonies of Myxococcoides, along with several filamentous genera generally considered to represent cyanobacterial sheaths. In addition, the phosphorites and associated rocks have δ13Corg values in the range of −26.0 to −29.7‰ VPDB, consistent with photoautotrophic carbon fixation with the Rubisco enzyme. Close association of phosphorites with the Marinoan tillites in stratigraphic level supports a genetic link between deglaciation and phosphogenesis, at least for the Doushantuo occurrence. Our new data suggest that major cyanobacterial blooms probably took place in the terminal Proterozoic, which might have resulted in rapid scavenging of bioavailable phosphorus and massive accumulations of organic matter (OM). Within a redox-stratified intra-shelf basin, the OM-bound phosphorus could have liberated by microbial sulfate reduction and other anaerobic metabolisms and subsequently concentrated by Fe-redox pumping below the chemocline. Upwelling of the bottom waters or upward fluctuation of the chemocline might have brought P-enriched waters to the photic zone, where it was again scavenged by cyanobacteria through their EPS to be subsequently precipitated as francolite. The feedbacks between enhanced continental weathering, cyanobacterial blooms, carbon burial, and accelerated phosphorus cycle thus controlled the marine biogeochemical changes, which led to further oxygenation of the atmosphere and oceans, ultimately paving the way for the rise of metazoans

Perspectives for Positron Emission Tomography with RPCs

In this study we address the feasibility and main properties of a positron emission tomograph (PET) based on RPCs. The concept, making use of the converter-plate principle, takes advantage of the intrinsic layered structure of RPCs and its simple and economic construction. The extremely good time and position resolutions of RPCs also allow the TOF-PET imaging technique to be considered. Monte-Carlo simulations, supported by experimental data, are presented and the main advantages and drawbacks for applications of potential interest are discussed.Comment: Presented at "RPC2001-VI Workshop on Resistive Plate Chambers and Related Detectors", Coimbra, Portugal, 26-27 November 2001 (5 pages

Fragments of the earliest land plants

The earliest fossil evidence for land plants comes from microscopic dispersed spores. These microfossils are abundant and widely distributed in sediments, and the earliest generally accepted reports are from rocks of mid-Ordovician age (Llanvirn, 475 million years ago). Although distribution, morphology and ultrastructure of the spores indicate that they are derived from terrestrial plants, possibly early relatives of the bryophytes, this interpretation remains controversial as there is little in the way of direct evidence for the parent plants. An additional complicating factor is that there is a significant hiatus between the appearance of the first dispersed spores and fossils of relatively complete land plants (megafossils): spores predate the earliest megafossils (Late Silurian, 425 million year ago) by some 50 million years. Here we report the description of spore-containing plant fragments from Ordovician rocks of Oman. These fossils provide direct evidence for the nature of the spore-producing plants. They confirm that the earliest spores developed in large numbers within sporangia, providing strong evidence that they are the fossilized remains of bona fide land plants. Furthermore, analysis of spore wall ultrastructure supports liverwort affinities

Assessment of the face validity of two pain scales in Kenya: a validation study using cognitive interviewing

Background: Patients in sub-Saharan Africa commonly experience pain, which often is un-assessed and undertreated. One hindrance to routine pain assessment in these settings is the lack of a single-item pain rating scale validated for the particular context. The goal of this study was to examine the face validity and cultural acceptability of two single-item pain scales, the Numerical Rating Scale (NRS) and the Faces Pain Scale-Revised (FPS-R), in a population of patients on the medical, surgical, and pediatric wards of Moi Teaching and Referral Hospital in Kenya. Methods: Swahili versions of the NRS and FPS-R were developed by standard translation and back-translation. Cognitive interviews were performed with 15 patients at Moi Teaching and Referral Hospital in Eldoret, Kenya. Interview transcripts were analyzed on a question-by-question basis to identify major themes revealed through the cognitive interviewing process and to uncover any significant problems participants encountered with understanding and using the pain scales. Results: Cognitive interview analysis demonstrated that participants had good comprehension of both the NRS and the FPS-R and showed rational decision-making processes in choosing their responses. Participants felt that both scales were easy to use. The FPS-R was preferred almost unanimously to the NRS. Conclusions: The face validity and acceptability of the Swahili versions of the NRS and FPS-R has been demonstrated for use in Kenyan patients. The broader application of these scales should be evaluated and may benefit patients who currently suffer from pain

Parallelization of Kinetic Theory Simulations

Numerical studies of shock waves in large scale systems via kinetic simulations with millions of particles are too computationally demanding to be processed in serial. In this work we focus on optimizing the parallel performance of a kinetic Monte Carlo code for astrophysical simulations such as core-collapse supernovae. Our goal is to attain a flexible program that scales well with the architecture of modern supercomputers. This approach requires a hybrid model of programming that combines a message passing interface (MPI) with a multithreading model (OpenMP) in C++. We report on our approach to implement the hybrid design into the kinetic code and show first results which demonstrate a significant gain in performance when many processors are applied.Comment: 10 pages, 3 figures, conference proceeding

Resistant tissues of modern marchantioid liverworts resemble enigmatic Early Paleozoic microfossils

Absence of a substantial pretracheophyte fossil record for bryophytes (otherwise predicted by molecular systematics) poses a major problem in our understanding of earliest land-plant structure. In contrast, there exist enigmatic Cambrian–Devonian microfossils (aggregations of tubes or sheets of cells or possibly a combination of both) controversially interpreted as an extinct group of early land plants known as nematophytes. We used an innovative approach to explore these issues: comparison of tube and cell-sheet microfossils with experimentally degraded modern liverworts as analogues of ancient early land plants. Lower epidermal surface tissues, including rhizoids, of Marchantia polymorpha and Conocephalum conicum were resistant to breakdown after rotting for extended periods or high-temperature acid treatment (acetolysis), suggesting fossilization potential. Cell-sheet and rhizoid remains occurred separately or together depending on the degree of body degradation. Rhizoid break-off at the lower epidermal surface left rimmed pores at the centers of cell rosettes; these were similar in structure, diameter, and distribution to pores characterizing nematophyte cell-sheet microfossils known as Cosmochlaina. The range of Marchantia rhizoid diameters overlapped that of Cosmochlaina pores. Approximately 14% of dry biomass of Marchantia vegetative thalli and 40% of gametangiophores was resistant to acetolysis. Pre- and posttreatment cell-wall autofluorescence suggested the presence of phenolic compounds that likely protect lower epidermal tissues from soil microbe attack and provide dimensional stability to gametangiophores. Our results suggest that at least some microfossils identified as nematophytes may be the remains of early marchantioid liverworts similar in some ways to modern Marchantia and Conocephalum

New observations of Ambient Inclusion Trails (AITs) and pyrite framboids in the Ediacaran Doushantuo Formation, South China

Ambient Inclusion Trails (AITs) are intriguing microtubular structures that commonly occur in association with pyrite in Precambrian organic-rich cherts and phosphorites. They are thought to be created by the migration of pyrite or other crystal grains through a lithified substrate driven by pressure solution from the in situ thermal decomposition of organic matter. New phosphorite samples of the Ediacaran Doushantuo Formation (South China) contain abundant AITs exhibiting diverse morphotypes, which may be distinguished from filamentous microfossils and endolithic microborings with a suite of morphological criteria based on optical microscopy and scanning electron microscopy (SEM). Black shales of the Baizhu section contains abundant pyrite framboids whose size distributions reveal significant temporal variations of redox conditions in shallow marine waters that probably promoted the formation of the Doushantuo phosphorites. AITs in the phosphorites are categorized into three types and further into five subtypes (I-a, I-b, II-a, II-b, and III) based on their morphologies and observed or interpreted associations with various kinds of terminal pyrite crystals. Among these, subtype II-a, single striated microtubes 2–10 μm wide, are interpreted to have resulted from migration of intact pyrite framboids. Those of subtype II-b, dense clusters of outward radiating microtubes with consistent widths and inward-facing cuspate ridges, likely have formed by explosive disintegration and propulsion of pyrite framboids due to highly concentrated carbon dioxide gas during the oxidation of organic matter. During early diagenesis, formation of euhedral and framboidal pyrites involve a suite of biogeochemical and physical processes including non-biological oxidation of organic matter and reduction of sulfate in the presence of ferrous iron. Following the burial of pyrites, further oxidative degradation of organic matter produced abundant CO2 gas, which drives the pyrites to move through the solid, but not yet fully lithified phosphatic gel composing granules. This model explains the formation of previously reported but unexplained star-burst type AITs and it may be tested by experimental studies. Our new observations provide evidence for the widespread occurrence of AITs in the Doushantuo phosphorites and urge careful petrographic examinations and differentiation between AITs and morphologically similar biogenic microstructures

Paleoecology and Phylogenetics of an Hirnantian Freshwater Palynological Assemblage from the Arabian Plate

peer reviewe

Prevalence and Correlates of Pain and Pain Treatment in a Western Kenya Referral Hospital

Background: Pain is often inadequately evaluated and treated in sub-Saharan Africa (SSA). Objective: We sought to assess pain levels and pain treatment in 400 hospitalized patients at a national referral hospital in western Kenya, and to identify factors associated with pain and pain treatment. Design: Using face-validated Kiswahili versions of two single-item pain assessment tools, the Numerical Rating Scale (NRS) and the Faces Pain Scale–Revised (FPS-R), we determined patients' pain levels. Additional data collected included patient demographics, prescribed analgesics, and administered analgesics. We calculated mean pain ratings and pain management index (PMI) scores. Results: Averaged between the NRS and FPS-R, 80.5% of patients endorsed a nonzero level of pain and 30% of patients reported moderate to severe pain. Older patients, patients with HIV, and cancer patients had higher pain ratings. Sixty-six percent of patients had been prescribed analgesics at some point during their hospitalization, the majority of which were nonopioids. A majority of patients (66%) had undertreated pain (negative scores on the PMI). Conclusion: This study shows that hospitalized patients in Kenya are experiencing pain and that this pain is often undertreated