ABSTRACT
Binary neutron star mergers are thought to be one of the dominant sites of production for rapid neutron capture elements, including platinum and gold. Since the discovery of the binary ...neutron star merger GW170817, and its associated kilonova AT2017gfo, numerous works have attempted to determine the composition of its outflowing material, but they have been hampered by the lack of complete atomic data. Here, we demonstrate how inclusion of new atomic data in synthetic spectra calculations can provide insights and constraints on the production of the heaviest elements. We employ theoretical atomic data (obtained using $\small {\rm GRASP}^{0}$) for neutral, singly and doubly ionized platinum and gold, to generate photospheric and simple nebular phase model spectra for kilonova-like ejecta properties. We make predictions for the locations of strong transitions, which could feasibly appear in the spectra of kilonovae that are rich in these species. We identify low-lying electric quadrupole and magnetic dipole transitions that may give rise to forbidden lines when the ejecta becomes optically thin. The strongest lines lie beyond 8000 Å, motivating high quality near-infrared spectroscopic follow-up of kilonova candidates. We compare our model spectra to the observed spectra of AT2017gfo, and conclude that no platinum or gold signatures are prominent in the ejecta. From our nebular phase modelling, we place tentative upper limits on the platinum and gold mass of ≲ a few 10−3 M⊙, and ≲ 10−2 M⊙, respectively. This work demonstrates how new atomic data of heavy elements can be included in radiative transfer calculations, and motivates future searches for elemental signatures.
Soils in tropical and temperate locations are known to be a sink for the genetic potential of anthropogenic-driven acquired antibiotic resistance (AR). In contrast, accumulation of acquired AR is ...less probable in most Polar soils, providing a platform for characterizing background resistance and establishing a benchmark for assessing AR spread. Here, high-throughput qPCR and geochemistry were used to quantify the abundance and diversity of both antibiotic resistance genes (ARGs) and selected mobile genetic elements (MGEs) across eight soil clusters in the Kongsfjorden region of Svalbard in the High Arctic. Relative ARG levels ranged by over two orders of magnitude (10−6 to 10−4 copies/16S rRNA gene copy), and showed a gradient of potential human and wildlife impacts across clusters as evidenced by altered geochemical conditions and increased “foreign” ARG abundances (i.e., allochthonous), including blaNDM-1. Impacted clusters exhibited 100× higher total ARGs and MGEs in tandem with elevated secondary nutrients, especially available P that is typically low and limiting in Arctic soils. In contrast, ARGs in less-impacted clusters correlated strongly to local soil lithology. The most plausible source of exogenous P and allochthonous ARGs in this region is bird and other wildlife guano, disseminated either by local human wastes or via direct carriage and deposition. Regardless of pathway, accumulation of apparent allochthonous ARGs and MGEs in High Arctic soils is concerning, highlighting the importance of characterizing Arctic sites now to establish benchmarks for tracking AR spread around the world.
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•High Arctic soils provide a benchmark for antibiotic resistance (AR) in nature.•Arctic landscapes help delineate putative autochthonous vs allochthonous AR genes.•Lithology defines AR gene abundance and diversity in “unimpacted” Arctic soils.•Fecal inputs define AR genes at “impacted” sites, overriding lithological control.•Multi-AR genes moved from temperate zones to the High Arctic in >three years.
Anaesthetic-induced developmental neurotoxicity (AIDN) has been clearly established in laboratory animal models. The possibility of neurotoxicity during uneventful anaesthetic procedures in human ...neonates or infants has led to serious questions about the safety of paediatric anaesthesia. However, the applicability of animal data to clinical anaesthesia practice remains uncertain. The spectre of cerebral injury due to cerebral hypoperfusion, metabolic derangements, coexisting disease, and surgery itself further muddles the picture. Given the potential magnitude of the public health importance of this issue, the clinician should be cognisant of the literature and ongoing investigations on AIDN, and raise awareness of the risks of both surgery and anaesthesia.
Abstract
The detection of a gravitational-wave signal and subsequent electromagnetic transient from a neutron star merger in 2017 is consistent with expectations of neutron star mergers as an
r
...-process element production site. Within the first few days post-merger, the kilonova spectra are consistent with a blackbody illuminating a mix of heavy,
r
-process elements. With increasing time, the kilonova transitions to the non-LTE regime where the level populations and ionization balance are determined by both collisional and photoprocesses. Detailed cross section data for electron-impact processes involving the relevant species are often not available. In such circumstances, it is reasonable to use approximate methods as baseline data for use in spectral modeling, and it is useful to evaluate the accuracy of such methods against more sophisticated collision calculations when possible. We describe new calculations of the electron-impact excitation cross sections of Pt
i
–
iIi
using the DARC
R
-matrix codes. Using collisional-radiative models, we show that, at plasma conditions expected in kilonovae, the expressions of van Regemorter and Axelrod are insufficient for producing electron-impact excitation data for complex, heavy species such as the low charge states of Pt. Through comparisons with data generated with the relativistic distorted wave approach, as implemented in the Flexible Atomic Code, we show the distorted wave method produces cross section data that, when incorporated into spectral models, predicts strong spectral feature distributions similar in intensity to those from models built on data computed with the
R
-matrix approach for the considered ions and plasma conditions.
New developments in laser ablation have shown great potential as nanofabrication methodologies, offering many significant advantages over more traditional methods. Herein, we have developed a method ...for applying two of these techniques, confined atmospheric pulsed-laser (CAP) deposition and laser ablation synthesis in solution (LASiS), to the fabrication of a nanostructured sensor platform. Following deposition, additional steps were then used to crosslink the deposited nanostructures and fabricate counter and reference electrodes. Chronoamperometry and cyclic voltammetry (CV) were used to assess the effects of these crosslinking steps on the properties of the sensor surfaces. These experiments resulted in the development of a simple, inexpensive and readily scalable process for the fabrication of 3-electrode sensor systems. As an example of a readily measurable surface interaction, electrochemical impedance spectroscopy (EIS) was applied to demonstrate the use of these systems in the detection of 6-mercaptohexanol. This interaction was examined in real-time by measuring the change in the EIS of the sensor system over time following its exposure to the thiol. This experiment clearly showed a measurable EIS response, demonstrating the effectiveness of these newly fabricated sensors for the detection of a simple surface interaction and suggesting the future potential of these laser based methods as the basis for an inexpensive, facile, rapid and scalable sensor fabrication process.
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•Development of a novel, inexpensive, scalable, laser based method for the fabrication of nanostructured biosensors.•Comparison of several sensor designs from various stages of the development process.•Demonstration of basic sensor activity using chronoamperometry and electrochemical impedance spectroscopy.•Examination of the effects of a key fabrication step on the properties of the sensor surface.
While preserving water quality by contracting with farmers has been examined previously, we analyze these arrangements from a different perspective. This study uses a transaction cost framework, in ...conjunction with detailed case studies of two water quality payment schemes, to examine factors that increase and decrease transaction costs in order to improve policy choice as well as policy design and implementation. In both the Munich and New York City cases, agreements with farmers to change land management practices resolved the water quality problems. In Munich, factors including lack of rural/urban antipathy, homogeneous land use, utilization of well-developed organic standards, and strong demand for organic products decreased transaction costs. Using existing organic institutions addressed a range of environmental issues simultaneously. Factors that decreased transaction costs in both cases included: highly sensitive land was purchased outright and the existence of one large “buyer”. Adequate lead time and flexibility of water quality regulations allowed negotiation and development of the watershed programs. Tourism and eco-labels allow urban residents to become aware of the agricultural production practices that affect their water supply. We conclude with recommendations based on the experiences of these cities, both of which have been proposed as models for other schemes.
► We compare approaches for nonpoint source water pollution in New York and Munich. ► We identify factors affecting transaction costs of contracting for ecosystem services. ► Using existing institutions, such as organic certification, reduces transaction costs. ► Homogeneous agents and a monopsony structure can decrease transaction costs.
A selection of electron-impact excitation
R
-matrix calculations completed by the collision group at Queens University Belfast are discussed. The atomic data calculated are the foundation of ...applications in a variety of fields, a sample of which are presented here. They include an analysis of Fe
ii
emission in active galactic nuclei, the possible presence of Pt and Au in the spectra of binary neutron star mergers and the viability of W ions as a diagnostic tool in magnetically confined tokamak plasmas. The radiative atomic data were computed using the most recent version of the fully relativistic structure code
grasp0
and the collision cross sections were evaluated using the recently developed
pdarc
R
-matrix package.
Graphic abstract
Cell wall architecture plays a key role in the regulation of plant cell growth and differentiation into specific cell types. Gaining genetic control of the amount, composition, and structure of cell ...walls in different cell types will impact both the quantity and yield of fermentable sugars from biomass for biofuels production. The recalcitrance of plant biomass to degradation is a function of how polymers crosslink and aggregate within walls. Novel imaging technologies provide an opportunity to probe these higher order structures in their native state. If cell walls are to be efficiently deconstructed enzymatically to release fermentable sugars, then we require a detailed understanding of their structural organization in future bioenergy crops.
In principle, the absolute configuration (AC) of a chiral molecule can be deduced from its optical rotation (OR) and/or its electronic circular dichroism (ECD). In practice, this requires reliable ...methodologies for predicting OR and ECD. The recent application of ab initio time-dependent density functional theory (TDDFT) to the calculation of transparent spectral region OR and ECD has greatly enhanced the reliability with which these phenomena can be predicted. TDDFT calculations of OR and ECD are being increasingly utilized in determining ACs. Nevertheless, such calculations are not perfect, and as a result, ACs determined are not 100% reliable. In this paper, we examine the reliability of the TDDFT methods in the case of chiral alkenes. Sodium d line specific rotations, αD, are predicted for 26 conformationally rigid alkenes of known AC, ranging in size from 5 to 20 C atoms, and with αD values in the range of 0−500. The mean absolute deviation of predicted αD values from experimental values is 28.7. With one exception, β-pinene, the signs of αD are correctly predicted. Errors in calculated αD values are approximately random. Our results define a “zone of indeterminacy” within which calculated αD values cannot be used to determine ACs with >95% confidence. TDDFT ECD spectra are predicted for eight of the alkenes and compared to experimental spectra. Agreement ranges from modestly good to poor, leading to the conclusion that TDDFT calculations of ECD spectra are not yet of sufficient accuracy to routinely provide highly reliable ACs. TDDFT OR calculations for two conformationally flexible alkenes, 3-tert-butylcyclohexene and trans-4-carene, are also reported. For the former, predicted rotations are incorrect in sign over the range 589−365 nm. It is possible that the AC of this molecule has been incorrectly assigned.
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