Large Offsets Research Articles

(Invited) Where are the Best Insulators for 2D Field-Effect Transistors?

Two-dimensional (2D) semiconductors are very promising for applications in next-generation field-effect transistors (FETs) which could overcome scaling limitations of Si technologies and thus extend the life of Moore’s law. The success at achieving this ambitious goal will depend on the availability of compatible insulators which are always required to separate the gate from the channel. Ideally, these insulators should go along with 2D semiconductors as well as SiO2 goes with Si. However, the research community is mostly focused on 2D semiconductors while not paying enough attention to finding suitable insulators for 2D FETs. In order to shed some light on this problem, here we formulate general requirements for insulators in 2D FETs and discuss the potential of already used and promising materials.The scaling potential of 2D FETs can be fully exploited only if high quality insulators with an equivalent oxide thickness (EOT) below 1nm are available, as required for low subthreshold swings and reduced power consumption. This results in the following requirements for gate insulators: First, dielectric properties have to be good enough to maintain low tunnel and thermionic leakage currents to achieve high on/off current ratios. This implies high dielectric constants, wide band gaps and large band offsets with the channel material. Second, the insulator must form a well-defined interface with the channel, which is primarily required for a high mobility. Third, the number of active insulator defects within a few nanometers from the interface has to be low, in order to reduce charge trapping and thus maintain high stability of device operation. Finally, the insulators have to be electrically stable when scaled and survive electric fields of at least 10MV/cm.Most previously reported 2D FETs employ conventional oxides (e.g. SiO2, HfO2, Al2O3) known from Si technologies. High-k oxides HfO2 and Al2O3 appear to be the most promising, as they in principle satisfy the requirement on low leakage currents. However, they are amorphous when grown in thin layer, thus forming poor-quality interfaces with 2D channels, and contain numerous unavoidable insulator defects which lead to hysteresis and long-term drifts of the gate transfer characteristics. As a result, it appears to be unlikely that these materials can be considered promising for applications in future fully scalable 2D FETs.In the spirit of Si technologies, a possible alternative to conventional oxides could be oxidation of 2D semiconductors to form native oxides, such as MoO3 from MoS2. However, many of these materials have fundamentally narrow bandgaps of 3-4 eV, while some of them are also non-stoichiometric due to the lack of well-adjusted oxidation methods and thus have a limited dielectric stability. Thus, considerable research efforts are still required to understand their potential.Another possible solution is the use of layered 2D insulators. Their main advantage is their crystalline structure which leads to well-defined interface with 2D semiconductors and a low density of insulator defects. However, the most widely used 2D insulator is hexagonal boron nitride (hBN) which has a narrow bandgap (6eV) and a small dielectric constant (less than 5). This makes it difficult to maintain low gate leakage currents for hBN with sub-1nm EOT. Thus, alternative 2D insulators have to be urgently identified and characterized. Among these materials are mica, which outperforms hBN in terms of dielectric properties, and 2D oxide nanosheets. However, considerable processing advances are required to result in the demonstration of real devices.Finally, another interesting option would be the use of ionic crystals, such as epitaxial fluorides (e.g. CaF2, BaF2, and LaF3). Similar to 2D insulators, fluorides ideally contain a small number of defects and form well-defined interfaces with 2D semiconductors. Also, in contrast to hBN, they have good dielectric properties, e.g. a bandgap of 12.1 eV and a dielectric constant of 8.43 for CaF2. Recently, excellent performance of MoS2 FETs with 2nm thick epitaxial CaF2 (0.9nm EOT) has been achieved, which is currently impossible with any other insulator discussed above. Thus, further research on these insulators appears a very promising way for the development of scalable 2D FETs.In summary, the question about the most promising insulators for 2D FETs is still open. However, already now it is clear that successful integration of amorphous oxides into these devices appears problematic. Thus, it can be concluded that high-quality 2D FETs require crystalline insulators. These can be either layered 2D or ionic crystals with chemically inert surfaces, which generally address the fundamental limitations of oxides. Further research on these materials should target those which have the best dielectric properties and can be synthesized using fully scalable methods.

Approximations for traveltime, slope, curvature, and geometric spreading of elastic waves in layered transversely isotropic media

Each seismic body wave, including quasi-, P-, S-, and converted wave modes, carries useful subsurface information. For the processing, imaging, amplitude analysis, and forward modeling of each wave mode, we need approximate equations of the traveltime, slope (ray parameter), and curvature as a function of offset. Considering the large offset coverage of modern seismic acquisitions, we have developed new approximations designed to be accurate at zero and infinitely large offsets over layered transversely isotropic media with vertical symmetry axis. Our approximation for traveltime is a modified version of the extended generalized moveout approximation that comprises six parameters. Our direct approximations for the ray parameter and curvature use new algebraically simple equations with three parameters. We define these parameters for each wave mode without ray tracing so that we have similar approximate equations for all wave modes that only change based on the parameter definitions. However, our approximations are unable to reproduce S-wave triplications that may occur in some strongly anisotropic models. Using our direct approximation of traveltime derivatives, we also obtain a new expression for the relative geometric spreading. We determine the high accuracy of our approximations using numerical tests on a set of randomly generated multilayer models. Using synthetic data, we show simple applications of our approximations for the normal moveout correction and relative geometric spreading compensation of different wave modes.

Supramolecular Perspective of Coordination Effects on Fluorine Interactions

Coordination effects have been considered through the most common interactions in the crystal structures of fluoro compounds (C–H/F and F/F interactions). The supramolecular profile of these effects is based on quantum-chemical calculations for the assessment of the interaction strength and electrostatic potential maps, which provide a qualitative insight into the examined effect. Coordination of aliphatic fluorides leads to an increase of the negative potential of the F atoms, and, hence, an increase in the hydrogen-bonding acceptor ability (strengthening of C–H/F interactions) and a weakening of the F/F interactions, due to an increase in repulsive interactions between the F atoms. There is no significant change in the potential of the F atoms due to coordination of C6-aromatic fluorides, as in the case of aliphatic ones. This results in slight changes in the strengths of the C–H/F and F/F interactions (coupled with parallel interaction at large offsets, PILO), in a noticeable enhancement of stacking interactions, as well as in a significant enhancement of interactions involving the π-system (F/π and C–H/π interactions). It has also been shown that a decrease in the charge of the metal ions leads to a decrease in the negative potential of the F atom and also that the nature of the metal ion has a significant influence on the value of the potential of the F atoms.

2.5D multifocusing imaging of crooked-line seismic surveys

Two-dimensional seismic surveys often are conducted along crooked-line traverses due to the inaccessibility of rugged terrains, logistical and environmental restrictions, and budget limitations. The crookedness of line traverses, irregular topography, and complex subsurface geology with steeply dipping and curved interfaces could adversely affect the signal-to-noise-ratio of the data. The crooked-line geometry violates the assumption of a straight-line survey that is a basic principle behind the 2D multifocusing (MF) method and leads to crossline spread of midpoints. In addition, the crooked-line geometry can give rise to potential pitfalls and artifacts and thus leads to difficulties in imaging and velocity-depth model estimation. We develop a novel MF algorithm for crooked-line seismic data and revise the traveltime equation accordingly to achieve better signal alignment before stacking. Specifically, we have developed a 2.5D MF reflection traveltime equation that explicitly takes into account the midpoint dispersion and cross-dip effects. The new formulation corrects for normal, inline, and crossline dip moveouts (DMOs) simultaneously, which is significantly more accurate than removing these effects sequentially. Applying normal moveout, DMO, and cross-DMO separately tends to result in significant errors, especially for large offsets. The 2.5D MF method can perform automatically with a coherence-based global optimization search on data. We investigated the accuracy of the new formulation by testing it on different synthetic models and a real seismic data set. Applying our approach to the real data led to a high-resolution seismic image with a significant quality improvement compared to the conventional method. Numerical tests indicate that the new formula can accurately focus the primary reflections at their correct location, remove anomalous dip-dependent velocities, and extract true dips from seismic data for structural interpretation. Our method efficiently projects and extracts valuable 3D structural information when applied to crooked-line seismic surveys.

The DUVET Survey: Direct T e -based Metallicity Mapping of Metal-enriched Outflows and Metal-poor Inflows in Markarian 1486

Abstract We present electron temperature (T e ) maps for the edge-on system Mrk 1486, affording “direct-method” gas-phase metallicity measurements across 5.″8 (4.1 kpc) along the minor axis and 9.″9 (6.9 kpc) along the major axis. These maps, enabled by strong detections of the [O iii] λ4363 auroral emission line across a large spatial extent of Mrk 1486, reveal a clear negative minor-axis T e gradient in which temperature decreases with increasing distance from the disk plane. We find that the lowest metallicity spaxels lie near the extremes of the major axis, while the highest metallicity spaxels lie at large spatial offsets along the minor axis. This is consistent with a picture in which low-metallicity inflows dilute the metallicity at the edges of the major axis of the disk, while star formation drives metal-enriched outflows along the minor axis. We find that the outflow metallicity in Mrk 1486 is 0.20 dex (1.6 times) higher than the average insterstellar medium (ISM) metallicity, and more than 0.80 dex (6.3 times) higher than metal-poor inflowing gas, which we observe to be below 5% Z ⊙. This is the first example of metallicity measurements made simultaneously for inflowing, outflowing, and inner disk ISM gas using consistent T e -based methodology. These measurements provide unique insight into how baryon-cycle processes contribute to the assembly of a galaxy like Mrk 1486.

Robust K-means algorithm with weighted window for seismic facies analysis

Abstract Seismic facies analysis can generate a map to describe the spatial distribution characteristics of reservoirs, and therefore plays a critical role in seismic interpretation. To analyse the characteristics of the horizon of interest, it is usually necessary to extract seismic waveforms along the target horizon using a selected time window. The inaccuracy of horizon interpretation often produces some inconsistent phases and leads to inaccurate classification. Therefore, the developed adaptive phase K-means algorithm proposed a sliding time window to extract seismic waveforms. However, setting the maximum offset of the sliding window is difficult in a real data application. A value that is too large may cause the cross-layer problem, whereas a value that is too small reduces the flexibility of the algorithm. To address this disadvantage, this paper proposes a robust K-means (R-K-means) algorithm with a Gaussian-weighted sliding window for seismic waveform classification. The used weights punish those windows distant from the interpretation horizon in the objective function, consequently producing a smaller range of horizon adjustments even when using relatively large maximum offsets and benefitting the generation of stable and reliable seismic facies maps. The application of real seismic data from the F3 block proves the effectiveness of the proposed algorithm.

Extended imaging volume in cone-beam x-ray tomography using the weighted simultaneous iterative reconstruction technique

An issue in computerized x-ray tomography is the limited size of available detectors relative to objects of interest. A solution was provided in the past two decades by positioning the detector in a lateral offset position, increasing the effective field of view (FOV) and thus the diameter of the reconstructed volume. However, this introduced artifacts in the obtained reconstructions, caused by projection truncation and data redundancy. These issues can be addressed by incorporating an additional data weighting step in the reconstruction algorithms, known as redundancy weighting. In this work, we present an implementation of redundancy weighting in the widely-used simultaneous iterative reconstruction technique (SIRT), yielding the weighted SIRT (W-SIRT) method. The new technique is validated using geometric phantoms and a rabbit specimen, by performing both simulation studies as well as physical experiments. The experiments are carried out in a highly flexible stereoscopic x-ray system equipped with x-ray image intensifiers (XRIIs). The simulations showed that higher values of contrast-to-noise ratio could be obtained using the W-SIRT approach as compared to a weighted implementation of the simultaneous algebraic reconstruction technique (SART). The convergence rate of the W-SIRT was accelerated by including a relaxation parameter in the W-SIRT algorithm, creating the aW-SIRT algorithm. This allowed to obtain the same results as the W-SIRT algorithm, but at half the number of iterations, yielding a much shorter computation time. The aW-SIRT algorithm has proven to perform well for both large as well as small regions of overlap, outperforming the pre-convolutional Feldkamp–David–Kress algorithm for small overlap regions (or large detector offsets). The experiments confirmed the results of the simulations. Using the aW-SIRT algorithm, the effective FOV was increased by >75%, only limited by experimental constraints. Although an XRII is used in this work, the method readily applies to flat-panel detectors as well.

Electronic properties of intrinsic vacancies in single-layer CaF2 and its heterostructure with monolayer MoS2

Exploring gate insulator materials for 2D transistors and their defect properties is of importance for device performance optimization. In this work, the structural and electronic properties of intrinsic vacancies in the CaF2 single layer and its heterostructures with monolayer MoS2 are investigated from first-principles calculations. VCa introduces a shallow defect level close to the VBM, whereas VF introduces a deep level below the CBM. In both cases, spin polarization is observed. Overall, VF has a relatively lower formation energy than VCa, except for the extreme Ca-rich case. Thus, VF should be dominant in CaF2. The band offset between CaF2 and MoS2 is determined to be type-I, with large offsets at both the conduction band and valence band. With the presence of vacancies in CaF2, the type-I band offset is preserved. The electron or hole on the defect states will transfer from CaF2 to MoS2 due to the large band offset, and spin polarization vanishes. Nevertheless, there are no defect states inside the gap or around the band edge of MoS2, and the electronic properties of MoS2 are almost intact. Compared with h-BN that has a small valence band offset with MoS2 and could introduce in-gap defect states, CaF2 can be a good candidate to serve as the dielectric layer of MoS2-based transistors.

Biases in parameter estimation from overlapping gravitational-wave signals in the third-generation detector era

In the past few years, the detection of gravitational waves from compact binary coalescences with the Advanced LIGO and Advanced Virgo detectors has become routine. Future observatories will detect even larger numbers of gravitational-wave signals, which will also spend a longer time in the detectors' sensitive band. This will eventually lead to overlapping signals, especially in the case of Einstein Telescope (ET) and Cosmic Explorer (CE). Using realistic distributions for the merger rate as a function of redshift as well as for component masses in binary neutron star and binary black hole coalescences, we map out how often signal overlaps of various types will occur in an ET-CE network over the course of a year. We find that a binary neutron star signal will typically have tens of overlapping binary black hole and binary neutron star signals. Moreover, it will happen up to tens of thousands of times per year that two signals will have their end times within seconds of each other. In order to understand to what extent this would lead to measurement biases with current parameter estimation methodology, we perform injection studies with overlapping signals from binary black hole and/or binary neutron star coalescences. Varying the signal-to-noise ratios, the durations of overlap, and the kinds of overlapping signals, we find that in most scenarios the intrinsic parameters can be recovered with negligible bias. However, we find large offsets for a short binary black hole or a quieter binary neutron star signal overlapping with a long and louder binary neutron star event when the merger times are sufficiently close. Although based on a limited number of simulations, our studies may be an indicator of where improvements are required to ensure reliable estimation of source parameters for all detected compact binary signals as we go from second-generation to third-generation detectors.

ΔO2/N2′ as a New Tracer of Marine Net Community Production: Application and Evaluation in the Subarctic Northeast Pacific and Canadian Arctic Ocean

We compared field measurements of the biological O2 saturation anomalies, ΔO2/Ar and ΔO2/N2, from simultaneous oceanographic deployments of a membrane inlet mass spectrometer and optode/gas tension device (GTD). Data from the Subarctic Northeast Pacific and Canadian Arctic Ocean were used to evaluate ΔO2/N2 as an alternative to ΔO2/Ar for estimates of mixed layer net community production (NCP). We observed strong spatial coherence between ΔO2/Ar and ΔO2/N2, with small offsets resulting from differences in the solubility properties of Ar and N2 and their sensitivity to vertical mixing fluxes. Larger offsets between the two tracers were observed across hydrographic fronts and under elevated sea states, resulting from the differential time-response of the optode and GTD, and from bubble dissolution in the ship’s seawater lines. We used a simple numerical framework to correct for physical sources of divergence between N2 and Ar, deriving the tracer ΔO2/N2′. Over most of our survey regions, ΔO2/N2′ provided a better analog for ΔO2/Ar, and thus more accurate NCP estimates than ΔO2/N2. However, in coastal Arctic waters, ΔO2/N2 and ΔO2/N2′ performed equally well as NCP tracers. On average, mixed layer NCP estimated from ΔO2/Ar and ΔO2/N2′ agreed to within ∼2 mmol O2 m–2 d–1, with offsets typically smaller than other errors in NCP calculations. Our results demonstrate a significant potential to derive NCP from underway O2/N2 measurements across various oceanic regions. Optode/GTD systems could replace mass spectrometers for autonomous NCP derivation under many oceanographic conditions, thereby presenting opportunities to significantly expand global NCP coverage from various underway platforms.

Strain-tunable band alignment and band gap of GaSe/WTe2 heterojunction for water splitting and light-emitting

Van der Waals heterojunctions (vdWHs) based on transition metal dichalcogenides (TMDs) attract much attention due to their unique electrochemical and physical properties. However, most vdWHs in TMD family are type II with indirect band gap. For vdWHs in TMD family, it is difficult to obtain the direct band gap through band arrangement approaches, limiting their applications in optoelectronics and photocatalysis. In present work, a type-I GaSe/WTe2 heterojunction with direct band gap (1.13 eV) is found by first-principles calculations. We find that this heterojunction has dipoleallowed direct band gap transition and large band offsets, which are beneficial to light emission efficiency. The effects of strain on electronic structure and optical properties of GaSe/WTe2 heterojunction are investigated. We find that band gap of type-I GaSe/WTe2 heterojunction can be tuned in large range by strain and it is a promising platform to develop strain-tunable light-emitting device which can emit various wavelengths. The band alignment type of GaSe/WTe2 heterojunction can be tuned from type-I to type-II by strain. Our results show that, in type-II alignment, it has efficient photocatalyticactivity in water splitting and the photocatalytic efficiency can be enhanced by strain. We hope our work can make a contribution to exploring a strain-tuned platform for photocatalytic and light-emitting devices.

Feasibility of superabsorbent polymer recycling and reuse in disposable absorbent hygiene products

The objective of this work is to evaluate the life cycle impacts of recovering superabsorbent polymers from absorbent hygiene products (AHPs). AHPs, which include baby diapers, feminine hygiene products, and adult incontinence pads, have a considerable environmental impact. While convenient, the vast majority of these products, which typically contain combinations of polypropylene, polyethylene, elastics, cellulose, and superabsorbent polymers (SAPs), are single use. Current practice of AHP disposal results in the loss of valuable materials like SAPs, generation of large volumes of municipal solid waste, and increased manufacturing burdens. While recognition of AHP impacts is increasing, it is important to consider that the most significant life cycle impacts of AHPs stem from resource extraction and manufacturing, not disposal itself. The SAPs in these products are of particular importance as they contribute substantially to these upstream life cycle impacts. We aim to shed light on how we might lessen upstream impacts by focusing on the potential for SAP recovery and re-use.This research evaluates end-of-life options for baby diapers in Europe using a life cycle approach to explore alternative options to conventional disposal of AHPs. We analyze the environmental trade-offs under the following scenarios: 1) diaper disposal via landfill or incineration; 2) diaper recycling without SAP recovery; and 3) diaper recycling with theoretical SAP recovery. Each recycling scenario is analyzed under two allocation conditions for a total of five scenarios. Environmental impacts were modeled in the LCA software SimaPro using the ReCipe 2016 impact assessment framework. Results show that SAP recovery has potential to decrease life cycle emissions by 54% compared to standard landfilling and incineration and by 35% when compared to the recycling technologies assessed in the study. SAP recovery and reuse also results in large potential offsets of energy and water burdens involved in SAP manufacturing. By assessing these environmental impacts, we aim to clarify the point at which SAP recovery demonstrates potential for circular economy.

LoTSS jellyfish galaxies

Context. The cluster environment has a strong impact on galaxy star formation, as seen by the fact that clusters host proportionally more red, passive galaxies relative to the field. Ram pressure stripping may drive this environmental quenching by directly stripping cold gas from galactic disks. In some cases, ram pressure stripping gives rise to ‘jellyfish galaxies’, observed with clear ‘tentacles’ of stripped gas extending beyond the optical extent of the galaxy. Aims. In this paper we present a large sample of jellyfish galaxies in low redshift clusters (z < 0.05), identified through 120−168 MHz radio continuum from the LOFAR Two-metre Sky Survey (LoTSS). Methods. From a parent sample of 29 X-ray-detected SDSS galaxy clusters and their spectroscopic members, we visually identify 95 star-forming, LoTSS jellyfish galaxies with 144 MHz radio tails. Star formation rates (SFRs) and stellar masses are obtained for all galaxies from SED fits. For each jellyfish galaxy we determine the tail orientation with respect to the cluster centre and quantify the prominence of the radio tails with the 144 MHz shape asymmetry. Results. After carefully accounting for redshift-dependent selection effects, we find that the frequency of jellyfish galaxies is relatively constant from cluster to cluster. LoTSS jellyfish galaxies are preferentially found at small clustercentric radius and large velocity offsets within their host clusters and have radio tails that are oriented away from the cluster centre. These galaxies also show enhanced star formation, relative to both ‘normal’ cluster galaxies and isolated field galaxies, but generally fall within the scatter of the L144 MHz − SFR relation. Conclusions. The properties of the LoTSS jellyfish galaxies identified in this work are fully consistent with expectations from ram pressure stripping. This large sample of jellyfish galaxies will be valuable for further constraining ram pressure stripping and star formation quenching in nearby galaxy clusters. We show that LOFAR is a powerful instrument for identifying ram pressure stripped galaxies across extremely wide fields. Moving forward, we will push the search for jellyfish galaxies beyond this initial cluster sample, including a comprehensive survey of the galaxy group regime.

Off-momentum cleaning simulations and measurements at the Large Hadron Collider

The Large Hadron Collider is designed to collide proton beams with unprecedented energy in order to extend the frontiers of high-energy physics. Particles that have an energy different from the nominal one follow dispersive orbits and, if the energy offset is large enough, could be lost on the cold aperture and cause quenches of superconducting magnets. Therefore, particles with large energy offsets must be removed from the beam by the collimation system. Although the dynamics of such particles is well understood and the efficiency of the momentum cleaning is evaluated in measurements, in the past, there were not general simulations tools available for predicting the efficiency of the collimation system in scenarios where off-momentum particles are involved. In this paper we present a new set of tools to simulate off-momentum losses, the benchmarking of these tools with measurements and the evaluation of off-momentum losses in the future LHC upgrade, the HL-LHC. These new simulation tools are applied for simulating two of the main scenarios where off-momentum particles play an important role in the LHC: particles lost at the start of the energy ramp and simulations of the momentum cleaning at 6.5 TeV energy. In this study, the collimation process during dynamic changes in the machine is simulated, as opposed to previous studies in static conditions. This is the first time that this sort of comparison between different simulation methods and measurements is performed. The results are used to provide a better understanding the dynamics of such particles and, finally, these tools are used to estimate the influence of off-momentum losses in the future High-Luminosity LHC.

The evaluation of the potential of global data products for snow hydrological modelling in ungauged high-alpine catchments

Abstract. For many ungauged mountain regions, global datasets of different meteorological and land surface parameters are the only data sources available. However, their applicability in modelling high-alpine regions has been insufficiently investigated so far. Therefore, we tested a suite of globally available datasets by applying the physically based Cold Regions Hydrological Model (CRHM) for a 10-year (September 2000–August 2010) period in the gauged high-alpine Research Catchment Zugspitze (RCZ), which is 12 km2 and located in the European Alps. Besides meteorological data, snow depth is measured at two stations. We ran CRHM with a reference run with in situ-measured meteorological data and a 2.5 m high-resolution digital elevation model (DEM) for the parameterization of the surface characteristics. Regarding different meteorological setups, we used 10 different globally available datasets (including versions of ERA, GLDAS, CFSR, CHIRPS) and additionally one transferred dataset from a similar station in the vicinity. Regarding the different DEMs, we used ALOS (Advanced Land Observing Satellite) and SRTM (Shuttle Radar Topography Mission) (both 30 m) as well as GTOPO30 (1 km). The following two main goals were investigated: (a) the reliability of simulations of snow depth, specific snow hydrological parameters and runoff with global meteorological products and (b) the influence of different global DEMs on snow hydrological simulations in such a topographically complex terrain. The range between all setups in mean decadal temperature is high at 3.5 ∘C and for the mean decadal precipitation sum at 1510 mm, which subsequently leads to large offsets in the snow hydrological results. Only three meteorological setups, the reference, the transferred in situ dataset and the CHIRPS dataset, substituting precipitation only, showed agreeable results when comparing modelled to measured snow depth. Nevertheless, those setups showed obvious differences in the catchment's runoff regime and in snow depth, snow cover, ablation period, the date, and quantity of maximum snow water equivalent in the entire catchment and in specific parts. All other globally available meteorological datasets performed worse. In contrast, all globally available DEM setups reproduced snow depth, the snow hydrological parameters and runoff quite well. Differences occurred mainly due to differences in radiation model input due to different spatial realizations. Even though SRTM and ALOS have the same spatial resolution, they showed considerable differences due to their different product origins. Despite the fact that the very coarse GTOPO30 DEM performed relatively well on the catchment mean, we advise against using this product in such heterogeneous high-alpine terrain since small-scale topographic characteristics cannot be captured. While global meteorological data are not suitable for sound snow hydrological modelling in the RCZ, the choice of the DEM with resolutions in the decametre level is less critical. Nevertheless, global meteorological data can be a valuable source to substitute single missing variables. For the future, however, we expect an increasing role of global data in modelling ungauged high-alpine basins due to further product improvements, spatial refinements and further steps regarding assimilation with remote sensing data.

An investigation of the IQM signal variation and error detection sensitivity for patient specific pre-treatment QA.

To evaluate the Integral Quality Monitor (IQM) as a clinical dosimetry device for detecting photon beam delivery errors in clinically relevant conditions. The IQM's ability to detect delivery errors introduced into clinical VMAT plans for two different treatment sites was assessed. This included measuring 103 nasopharynx VMAT plans and 78 lung SBRT VMAT plans with introduced errors in gantry angle (1-5°) and in MLC-defined field size and field shift (1-5mm). The IQM sensitivity was compared to ArcCheck detector performance. Signal dependence on field position for on-axis and asymmetrically offset square field sizes from 1×1cm2 to 30×30cm2 was also investigated. The IQM detected almost all introduced clinically-significant MLC field size errors, but not some small gantry angle errors or most MLC field shift errors. The IQM sensitivity was comparable to the ArcCheck for lung SBRT, but worse for the nasopharynx plans. Differences between IQM calculated/predicted and measured signals were within±2% for all on-axis square fields, but up to 60% for the smallest asymmetrically offset fields at large offsets. The IQM performance was consistent and reproducible. It showed highest sensitivity to the field size errors for these plans, but did not detect some clinically-significant introduced gantry angle errors or most MLC field shift errors. The IQM calculation model is still being developed, which should improve small offset-field performance. Care is required in IQM use for plan verification or online monitoring, especially for small fields that are off-axis in the detector gradient direction.

Compressing Over-the-Counter Markets

Over-the-counter markets are at the center of the global reform of the financial system. We show how the size and structure of these markets can undergo rapid and extensive changes when participants engage in portfolio compression, which is an optimization technology that exploits multilateral netting opportunities. We find that tightly knit and concentrated trading structures, as featured by many large over-the-counter markets, are especially susceptible to reductions of notional amounts and network reconfigurations resulting from compression activities. Using a unique transaction-level data set on credit-default-swaps markets, we estimate reduction levels, suggesting that the adoption of this technology can account for a large share of the historical development observed in these markets since the global financial crisis. Finally, we test the effect of a mandate to centrally clear over the counter markets in terms of size and structure. When participants engage in both central clearing and portfolio compression with the clearinghouse, we find large netting failures if clearinghouses proliferate. Allowing for compression across clearinghouses by and large offsets this adverse effect.

The Photometric Metallicity and Carbon Distributions of the Milky Way’s Halo and Solar Neighborhood from S-PLUS Observations of SDSS Stripe 82

Abstract We report photometric estimates of effective temperature, T eff, metallicity, [Fe/H], carbonicity, [C/Fe], and absolute carbon abundances, A(C), for over 700,000 stars from the Southern Photometric Local Universe Survey (S-PLUS) Data Release 2, covering a substantial fraction of the equatorial Sloan Digital Sky Survey Stripe 82. We present an analysis for two stellar populations: (1) halo main-sequence turnoff stars and (2) K-dwarf stars of mass 0.58 < M/M ⊙ < 0.75 in the Solar Neighborhood. Application of the Stellar Photometric Index Network Explorer (SPHINX) to the mixed-bandwidth (narrow- plus wide-band) filter photometry from S-PLUS produces robust estimates of the metallicities and carbon abundances in stellar atmospheres over a wide range of temperatures, 4250 < T eff(K) < 7000. The use of multiple narrow-band S-PLUS filters enables SPHINX to achieve substantially lower levels of “catastrophic failures” (i.e., large offsets in metallicity estimates relative to spectroscopic determinations) than previous efforts using a single metallicity-sensitive narrow-band filter. We constrain the exponential slope of the Milky Way’s K-dwarf halo metallicity distribution function (MDF), λ 10,[Fe/H] = 0.85 ± 0.21, over the metallicity range −2.5 < [Fe/H] < −1.0; the MDF of our local-volume K-dwarf sample is well-represented by a gamma distribution with parameters α = 2.8 and β = 4.2. S-PLUS photometry obtains absolute carbon abundances with a precision of ∼0.35 dex for stars with T eff < 6500 K. We identify 364 candidate carbon-enhanced metal-poor stars, obtain assignments of these stars into the Yoon–Beers morphological groups in the A(C)-[Fe/H] space, and we derive the CEMP frequencies.

Where are Mars’ Hypothesized Ocean Shorelines? Large Lateral and Topographic Offsets Between Different Versions of Paleoshoreline Maps

AbstractMars’ controversial hypothesized ocean shorelines have been found to deviate significantly from an expected equipotential surface. While multiple deformation models have been proposed to explain the wide range of elevations, here we show that the historical locations used in the literature and in these models vary widely. We find that the most commonly used version of the Arabia Level does not follow the originally described contact and can deviate laterally by ∼500 km in Deuteronilus Mensae. A meta‐analysis of different published maps shows that, globally, the minimum lateral offsets between the locations of the putative Arabia and Deuteronilus shorelines vary by an average of 141 ± 142 km and 180 ± 177 km, respectively. This leads to mean elevations of the Arabia Level that vary by up to 2.2 km between different mappings, and topographic ranges within each global mapping ranging from 2.7 to 7.7 km. The younger Deuteronilus Level has less topographic variation as it largely follows a formal contact (the Vastitas Borealis Formation) within the relatively flat northern plains. Given the high variance in position (spatial and topographic) of the maps, the use of such data and conclusions based on them are potentially problematic.

A giant molecular cloud catalogue in the molecular disc of the elliptical galaxy NGC 5128 (Centaurus A)

ABSTRACT We present the first census of giant molecular clouds (GMCs) complete down to 106 M⊙ and within the inner 4 kpc of the nearest giant elliptical and powerful radio galaxy, Centaurus A. We identified 689 GMCs using CO(1–0) data with 1 arcsec spatial resolution (∼20 pc) and 2 km s−1 velocity resolution obtained with the Atacama Large Millimeter/submillimeter Array. The I(CO)-N(H2) conversion factor based on the virial method is XCO = (2 ± 1) × 1020 cm−2(K km s−1)−1 for the entire molecular disc, consistent with that of the discs of spiral galaxies including the Milky Way, and XCO = (5 ± 2) × 1020 cm−2(K km s−1)−1 for the circumnuclear disc (CND; within a galactocentric radius of 200 pc). We obtained the GMC mass spectrum distribution and find that the best truncated power-law fit for the whole molecular disc, with index γ ≃ −2.41 ± 0.02 and upper cut-off mass $\sim \! 1.3\times 10^{7}\, \mathrm{M}_{\odot }$, is also in agreement with that of nearby disc galaxies. A trend is found in the mass spectrum index from steep to shallow as we move to inner radii. Although the GMCs are in an elliptical galaxy, the general GMC properties in the molecular disc are as in spiral galaxies. However, in the CND, large offsets in the line-width-size scaling relations (∼0.3 dex higher than those in the GMCs in the molecular disc), a different XCO factor, and the shallowest GMC mass distribution shape (γ = −1.1 ± 0.2) all suggest that there the GMCs are most strongly affected by the presence of the active galactic nucleus and/or shear motions.