Plate tectonics: When ancient continents collide

The geological record preserves scant evidence for early plate tectonics. Analysis of eclogites — metamorphic rocks formed in subduction zones — in the Trans-Hudson mountain belt suggests modern-style subduction may have operated 1,800 million years ago

The relationship between mantle potential temperature and oceanic lithosphere buoyancy

The Earth's mantle potential temperature (Tp) is thought to have cooled by ~250 °C since the Archean, causing a progressive change in both the structure and composition of oceanic lithosphere. These variables affect the negative buoyancy of subducting slabs, which is known to be an important force in driving plate motions. However, the relationship between Tp and slab buoyancy remains unclear. Here, we model the formation and subduction of oceanic lithosphere as a function of Tp, to investigate how Tp influences the buoyancy of subducting slabs, and by extension how buoyancy forces may have changed through time. First, we simulate isentropic melting of peridotite at mid-ocean ridges over a range of Tp (1300-1550 °C) to calculate oceanic lithosphere structure and composition. Second, we model the thermal evolution of oceanic plates undergoing subduction for a variety of scenarios (by varying lithospheric thickness, slab length and subduction velocity). Finally, we integrate the structural, compositional and thermal constraints to forward model subduction metamorphism of oceanic plates to determine down-going slab density structures. When compared with ambient mantle, these models allow us to calculate buoyancy forces acting on subducting slabs. Our results indicate that oceanic lithosphere derived from hotter mantle has a greater negative buoyancy, and therefore subduction potential, than lithosphere derived from cooler mantle for a wide range of subduction scenarios. With respect to the early Earth, this conclusion supports the viability of subduction, and models of subduction zone initiation that invoke the concept of oceanic lithosphere being primed to subduct. However, we also show that decreases to lithosphere thickness and slab length, and reduced crustal hydration, progressively reduce slab negative buoyancy. These results highlight the need for robust estimates of early Earth lithospheric properties when considering whether subduction was operative at this time. Nevertheless, our findings suggest that subduction processes on the early Earth may have been uniformitarian

Quantitative elemental mapping of granulite-facies monazite: Textural insights and implications for petrochronology

Texturally complex monazite grains contained in two granulite-facies pelitic migmatites from southern Baffin Island, Arctic Canada, were mapped by laser ablation-inductively coupled plasma-mass spectrometry (using spot sizes < 5 µm) to quantitatively determine the spatial variation in trace element chemistry (with up to 1883 analyses per grain). The maps highlight the chemical complexity of monazite grains that have experienced multiple episodes of growth, resorption and chemical modification by dissolution-precipitation during high-grade metamorphism. Following detailed chemical characterisation of monazite compositional zones, a related U-Pb dataset is re-interpreted, allowing petrologically-significant ages to be extracted from a continuum of concordant data. Synthesis of these data with pseudosection modelling of prograde and peak conditions allows for the temporal evolution of monazite trace element chemistry to be placed in the context of the evolving P-T conditions and major phase assemblage. This approach enables a critical evaluation of three commonly used petrochronological indicators: linking Y to garnet abundance, the Eu anomaly to feldspar content, and Th/U to anatectic processes. Europium anomalies and Th/U behave in a relatively systematic fashion, suggesting that they are reliable petrochronological witnesses. However, Y systematics are variable, both within domains interpreted to have grown in a single event, between grains interpreted to be part of the same age population, and between samples that experienced similar metamorphic conditions and mineral assemblages. These observations caution against generalised petrological interpretations on the basis of Y content, as it suggests Y concentrations in monazite are controlled by domainal equilibria. The results reveal a ~45 Myr interval between prograde metamorphism and retrograde melt crystallisation in the study area, emphasising the long-lived nature of heat flow in high-grade metamorphic terranes. Such long timescales of metamorphism would be assisted by the growth, retention and dominance of high-Th suprasolidus monazite, as observed in this study, contributing to the radiogenic heating budget of mid- to lower-crustal environments. Careful characterisation of monazite grains suggests that continuum-style U-Pb datasets can be decoded to provide insights into the duration of metamorphic processes.Natural Sciences and Engineering Research Council Visiting Fellowship Isaac Newton Trust Research Grant (RG74916

The College News, 1918-05-23, Vol. 04, No. 27

Bryn Mawr College student newspaper. Merged with The Haverford News in 1968 to form the Bi-college News (with various titles from 1968 on). Published weekly (except holidays) during the academic year

Cued to act on impulse: more impulsive choice and risky decision making by women susceptible to overeating after exposure to food stimuli

There is increasing evidence that individual differences in tendency to overeat relate to impulsivity, possibly by increasing reactivity to food-related cues in the environment. This study tested whether acute exposure to food cues enhanced impulsive and risky responses in women classified on tendency to overeat, indexed by scores on the three factor eating questionnaire disinhibition (TFEQ-D), restraint (TFEQ-R) and hunger scales. Ninety six healthy women completed two measures of impulsive responding (delayed discounting, DDT and a Go No-Go, GNG, task) and a measure of risky decision making (the balloon analogue risk task, BART) as well as questionnairemeasures of impulsive behaviour either after looking at a series of pictures of food or visually matched controls. Impulsivity (DDT) and risk-taking (BART) were both positively associated with TFEQ-D scores, but in both cases this effect was exacerbated by prior exposure to food cues. No effects of restraint were found. TFEQ-D scores were also related tomore commission errors on the GNG, while restrained women were slower on the GNG, but neither effect was modified by cue exposure. Overall these data suggest that exposure to food cues act to enhance general impulsive responding in women at risk of overeating and tentatively suggest an important interaction between tendency for impulsive decision making and food cues thatmay help explain a key underlying risk factor for overeating

Intestinal strongyloidiasis and hyperinfection syndrome

In spite of recent advances with experiments on animal models, strongyloidiasis, an infection caused by the nematode parasite Strongyloides stercoralis, has still been an elusive disease. Though endemic in some developing countries, strongyloidiasis still poses a threat to the developed world. Due to the peculiar but characteristic features of autoinfection, hyperinfection syndrome involving only pulmonary and gastrointestinal systems, and disseminated infection with involvement of other organs, strongyloidiasis needs special attention by the physician, especially one serving patients in areas endemic for strongyloidiasis. Strongyloidiasis can occur without any symptoms, or as a potentially fatal hyperinfection or disseminated infection. Th(2 )cell-mediated immunity, humoral immunity and mucosal immunity have been shown to have protective effects against this parasitic infection especially in animal models. Any factors that suppress these mechanisms (such as intercurrent immune suppression or glucocorticoid therapy) could potentially trigger hyperinfection or disseminated infection which could be fatal. Even with the recent advances in laboratory tests, strongyloidiasis is still difficult to diagnose. But once diagnosed, the disease can be treated effectively with antihelminthic drugs like Ivermectin. This review article summarizes a case of strongyloidiasis and various aspects of strongyloidiasis, with emphasis on epidemiology, life cycle of Strongyloides stercoralis, clinical manifestations of the disease, corticosteroids and strongyloidiasis, diagnostic aspects of the disease, various host defense pathways against strongyloidiasis, and available treatment options

In quest of a systematic framework for unifying and defining nanoscience

This article proposes a systematic framework for unifying and defining nanoscience based on historic first principles and step logic that led to a “central paradigm” (i.e., unifying framework) for traditional elemental/small-molecule chemistry. As such, a Nanomaterials classification roadmap is proposed, which divides all nanomatter into Category I: discrete, well-defined and Category II: statistical, undefined nanoparticles. We consider only Category I, well-defined nanoparticles which are >90% monodisperse as a function of Critical Nanoscale Design Parameters (CNDPs) defined according to: (a) size, (b) shape, (c) surface chemistry, (d) flexibility, and (e) elemental composition. Classified as either hard (H) (i.e., inorganic-based) or soft (S) (i.e., organic-based) categories, these nanoparticles were found to manifest pervasive atom mimicry features that included: (1) a dominance of zero-dimensional (0D) core–shell nanoarchitectures, (2) the ability to self-assemble or chemically bond as discrete, quantized nanounits, and (3) exhibited well-defined nanoscale valencies and stoichiometries reminiscent of atom-based elements. These discrete nanoparticle categories are referred to as hard or soft particle nanoelements. Many examples describing chemical bonding/assembly of these nanoelements have been reported in the literature. We refer to these hard:hard (H-n:H-n), soft:soft (S-n:S-n), or hard:soft (H-n:S-n) nanoelement combinations as nanocompounds. Due to their quantized features, many nanoelement and nanocompound categories are reported to exhibit well-defined nanoperiodic property patterns. These periodic property patterns are dependent on their quantized nanofeatures (CNDPs) and dramatically influence intrinsic physicochemical properties (i.e., melting points, reactivity/self-assembly, sterics, and nanoencapsulation), as well as important functional/performance properties (i.e., magnetic, photonic, electronic, and toxicologic properties). We propose this perspective as a modest first step toward more clearly defining synthetic nanochemistry as well as providing a systematic framework for unifying nanoscience. With further progress, one should anticipate the evolution of future nanoperiodic table(s) suitable for predicting important risk/benefit boundaries in the field of nanoscience

Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.

BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta