Heat-pipe Earth Moore, William B; Webb, A Alexander G
Nature (London),
09/2013, Volume:
501, Issue:
7468
Journal Article
Peer reviewed
The heat transport and lithospheric dynamics of early Earth are currently explained by plate tectonic and vertical tectonic models, but these do not offer a global synthesis consistent with the ...geologic record. Here we use numerical simulations and comparison with the geologic record to explore a heat-pipe model in which volcanism dominates surface heat transport. These simulations indicate that a cold and thick lithosphere developed as a result of frequent volcanic eruptions that advected surface materials downwards. Declining heat sources over time led to an abrupt transition to plate tectonics. Consistent with model predictions, the geologic record shows rapid volcanic resurfacing, contractional deformation, a low geothermal gradient across the bulk of the lithosphere and a rapid decrease in heat-pipe volcanism after initiation of plate tectonics. The heat-pipe Earth model therefore offers a coherent geodynamic framework in which to explore the evolution of our planet before the onset of plate tectonics.
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DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
The initiation mechanism of Earth’s plate tectonic cooling system remains uncertain. A growing consensus suggests that multi-plate tectonics was preceded by cooling through a single-plate ...lithosphere, but models for how this lithosphere was first broken into plates have not converged on a mechanism or a typical early plate scale. A commonality among prior efforts is the use of continuum mechanics approximations to evaluate this solid mechanics problem. Here we use 3D spherical shell models to demonstrate a self-organized fracture mechanism analogous to thermal expansion-driven lithospheric uplift, in which globe-spanning rifting occurs as a consequence of horizontal extension. Resultant fracture spacing is a function of lithospheric thickness and rheology, wherein geometrically-regular, polygonal-shaped tessellation is an energetically favored solution because it minimizes total crack length. Therefore, warming of the early lithosphere itself—as anticipated by previous studies—should lead to failure, propagating fractures, and the conditions necessary for the onset of multi-plate tectonics.
The clockwork of plant circadian oscillators has been resolved through investigations in Arabidopsis thaliana. The circadian oscillator is an important regulator of much of plant physiology, though ...many of the mechanisms are unclear. New findings demonstrate that the oscillator adjusts phase and period in response to abiotic and biotic signals, providing insight in to how the plant circadian oscillator integrates with the biology of the cell and entrains to light, dark and temperature cycles. We propose that the plant circadian oscillator is dynamically plastic, in constant adjustment, rather than being an isolated clock impervious to cellular events.
In a study of fluid resuscitation, patients received 6% hydroxyethyl starch (HES; 130/0.4) or saline until ICU discharge or death or for 90 days. There was no significant difference in 90-day ...mortality, although more patients in the HES group received renal-replacement therapy.
The administration of intravenous fluids to increase intravascular volume is a frequent intervention in the intensive care unit (ICU), but the choice of resuscitation fluid remains controversial.
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Globally, 0.9% sodium chloride (saline) is the most commonly used fluid, although colloids are administered as often as crystalloids, and hydroxyethyl starch (HES) is the most frequently used colloid.
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Several studies have questioned the safety of HES in critically ill patients, with particular concern that its use increases the risk of acute kidney injury.
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Most concern has focused on the use of concentrated HES solutions (10%) with a molecular weight of . . .
Circadian clocks provide a competitive advantage in an environment that is heavily influenced by the rotation of the Earth, by driving daily rhythms in behaviour, physiology and metabolism in ...bacteria, fungi, plants and animals. Circadian clocks comprise transcription-translation feedback loops, which are entrained by environmental signals such as light and temperature to adjust the phase of rhythms to match the local environment. The production of sugars by photosynthesis is a key metabolic output of the circadian clock in plants. Here we show that these rhythmic, endogenous sugar signals can entrain circadian rhythms in Arabidopsis thaliana by regulating the gene expression of circadian clock components early in the photoperiod, thus defining a 'metabolic dawn'. By inhibiting photosynthesis, we demonstrate that endogenous oscillations in sugar levels provide metabolic feedback to the circadian oscillator through the morning-expressed gene PSEUDO-RESPONSE REGULATOR 7 (PRR7), and we identify that prr7 mutants are insensitive to the effects of sucrose on the circadian period. Thus, photosynthesis has a marked effect on the entrainment and maintenance of robust circadian rhythms in A. thaliana, demonstrating that metabolism has a crucial role in regulation of the circadian clock.
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DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Background. Beta-lactam antibiotics are a commonly used treatment for severe sepsis, with intermittent bolus dosing standard therapy, despite a strong theoretical rationale for continuous ...administration. The aim of this trial was to determine the clinical and pharmacokinetic differences between continuous and intermittent dosing in patients with severe sepsis. Methods. This was a prospective, double-blind, randomized controlled trial of continuous infusion versus intermittent bolus dosing of piperacillin-tazobactam, meropenem, and ticarcillin-clavulanate conducted in 5 intensive care units across Australia and Hong Kong. The primary pharmacokinetic outcome on treatment analysis was plasma antibiotic concentration above the minimum inhibitory concentration (MIC) on days 3 and 4. The assessed clinical outcomes were clinical response 7–14 days after study drug cessation, ICU-free days at day 28 and hospital survival. Results. Sixty patients were enrolled with 30 patients each allocated to the intervention and control groups. Plasma antibiotic concentrations exceeded the MIC in 82% of patients (18 of 22) in the continuous arm versus 29% (6 of 21) in the intermittent arm (P = .001). Clinical cure was higher in the continuous group (70% vs 43%; P = .037), but ICU-free days (19.5 vs 17 days; P = .14) did not significantly differ between groups. Survival to hospital discharge was 90% in the continuous group versus 80% in the intermittent group (P = .47). Conclusions. Continuous administration of beta-lactam antibiotics achieved higher plasma antibiotic concentrations than intermittent administration with improvement in clinical cure. This study provides a strong rationale for further multicenter trials with sufficient power to identify differences in patient-centered endpoints.
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Photograph of a Halbach array containing 2948 individual magnets, operating at Larmor frequency of 2.15 MHz, with a homogeneity of 2400 ppm over a 20 cm diameter of spherical volume.
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...•A 23 ring Halbach array of permanent magnets has been designed to operate at 2.15 MHz.•Addition of shimming rings gives 2400 ppm homogeneity over a 20 cm diameter.•Three-dimensional images with a resolution of 3.5 × 3.5 × 3.5 mm have been acquired.
Modern clinical MRI systems utilise very high magnetic fields strengths to produce high resolution images of the human body. The high up-front and maintenance cost of these systems means that much of the world lacks access to this technology. In this paper we propose a low cost, head-only, homogenous Halbach magnet array with the potential for paediatric neuroimaging in low-resource settings. The homogeneity of the Halbach array is improved by allowing the diameter of the Halbach array to vary along its length, and also adding smaller internal shim magnets. The constructed magnet has a bore diameter of 27 cm, mean B0 field strength of 50.4 mT and a homogeneity of 2400 ppm over a 20 cm diameter spherical volume. The level of homogeneity of the system means that coil-based gradients can be used for spatial encoding which greatly increases the flexibility in image acquisition. 3D images of a “brain phantom” were acquired over a 22 × 22 × 22 cm field of view with a 3.5 mm isotropic resolution using a spin-echo sequence. Future development of a low-cost gradient amplifier and an open-source spectrometer has the potential of offering a fully open-source, low-cost MRI system for paediatric neuroimaging in low-resource settings.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Human health is dependent on a plentiful and nutritious supply of food, primarily derived from crop plants. Rhythmic supply of light as a result of the day and night cycle led to the evolution of ...circadian clocks that modulate most plant physiology, photosynthesis, metabolism, and development. To regulate crop traits and adaptation, breeders have indirectly selected for variation at circadian genes. The pervasive impact of the circadian system on crops suggests that future food production might be improved by modifying circadian rhythms, engineering the timing of transgene expression, and applying agricultural treatments at the most effective time of day. We describe the applied research required to take advantage of circadian biology in agriculture to increase production and reduce inputs.
Aims. In light of recent discoveries of pulsating ultraluminous X-ray sources (ULXs) and recently introduced theoretical schemes that propose neutron stars (NSs) as the central engines of ULXs, we ...revisit the spectra of eighteen well known ULXs, in search of indications that favour this newly emerging hypothesis. Methods. We examine the spectra from high-quality XMM-Newton and NuSTAR observations. We use a combination of elementary black body and multicolour disk black body (MCD) models, to diagnose the predictions of classic and novel theoretical models of accretion onto NSs. We re-interpret the well established spectral characteristics of ULXs in terms of accretion onto lowly or highly magnetised NSs, and explore the resulting parameter space for consistency. Results. We confirm the previously noted presence of the low-energy (≲6 keV) spectral rollover and argue that it could be interpreted as due to thermal emission. The spectra are well described by a double thermal model consisting of a “hot” (≳1 keV) and a “cool” (≲0.7 keV) multicolour black body (MCB). Under the assumption that the “cool” MCD emission originates in a disk truncated at the neutron star magnetosphere, we find that all ULXs in our sample are consistent with accretion onto a highly magnetised (B ≳ 1012 G) neutron star. We note a strong correlation between the strength of the magnetic field, the temperature of the “hot” thermal component and the total unabsorbed luminosity. Examination of the NuSTAR data supports this interpretation and also confirms the presence of a weak, high-energy (≳15 keV) tail, most likely the result of modification of the MCB emission by inverse Compton scattering. We also note that the apparent high-energy tail, may simply be the result of mismodelling of MCB emission with an atypical temperature (T) versus radius (r) gradient, using a standard MCD model with a fixed gradient of T ~ r-0.75. Conclusions. We have offered a new and robust physical interpretation for the dual-thermal spectra of ULXs. We find that the best-fit derived parameters of our model, are in excellent agreement with recent theoretical predictions that favour super-critically accreting NSs as the engines of a large fraction of ULXs. Nevertheless, the considerable degeneracy between models and the lack of unequivocal evidence cannot rule out other equally plausible interpretations. Deeper broadband observations and time-resolved spectroscopy are warranted to further explore this newly emerging framework.
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Coarse‐grained (CG) modeling is an invaluable tool for the study of polymers and other soft matter systems due to the span of spatiotemporal scales that typify their physics and behavior. Given ...continuing advancements in experimental synthesis and characterization of such systems, there is ever greater need to leverage and expand CG capabilities to simulate diverse soft matter systems with chemical specificity. In this review, we discuss essential modeling techniques, bottom‐up coarse‐graining methodologies, and outstanding challenges for the chemically specific CG modeling of polymer‐based systems. This methodologically oriented discussion is complemented by representative literature examples for polymer simulation; we also offer some advisory practical considerations that should be useful for new researchers. Given its growing importance in the modeling and polymer science community, we further highlight some recent applications of machine learning that enhance CG modeling strategies. Overall, this review provides comprehensive discussion of methods and prospects for the chemically specific coarse‐graining of polymers.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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