A machine learning model was created to predict the electron spectrum generated by a GeV-class laser wakefield accelerator. The model was constructed from variational convolutional neural networks, which mapped the results of secondary laser and plasma diagnostics to the generated electron spectrum. An ensemble of trained networks was used to predict the electron spectrum and to provide an estimation of the uncertainty of that prediction. It is anticipated that this approach will be useful for inferring the electron spectrum prior to undergoing any process that can alter or destroy the beam. In addition, the model provides insight into the scaling of electron beam properties due to stochastic fluctuations in the laser energy and plasma electron density.

Current sea-level rise partly stems from increased surface melting and meltwater runoff from the Greenland ice sheet. Multi-year snow, also known as firn, covers about 80% of the ice sheet and retains part of the surface meltwater. Since the firn cold content integrates its physical and thermal characteristics, it is a valuable tool for determining the meltwater-retention potential of firn. We use gap-filled climatological data from nine automatic weather stations in the ice-sheet accumulation area to drive a surface-energy-budget and firn model, validated against firn density and temperature observations, over the 1998–2017 period. Our results show a stable top 20 m firn cold content (CC20) at most sites. Only at the lower-elevation Dye-2 site did CC20 decrease, by 24% in 2012, before recovering to its original value by 2017. Heat conduction towards the surface is the main process feeding CC20 at all nine sites, while CC20 reduction occurs through low-cold-content fresh-snow addition at the surface during snowfall and latent-heat release when meltwater refreezes. Our simulations suggest that firn densification, while reducing pore space for meltwater retention, increases the firn cold content, enhances near-surface meltwater refreezing and potentially sets favourable conditions for ice-slab formation.

Glacier surface mass-balance measurements on Greenland started more than a century ago, but no compilation exists of the observations from the ablation area of the ice sheet and local glaciers. Such data could be used in the evaluation of modelled surface mass balance, or to document changes in glacier melt independently from model output. Here, we present a comprehensive database of Greenland glacier surface mass-balance observations from the ablation area of the ice sheet and local glaciers. The database spans the 123 a from 1892 to 2015, contains a total of ~3000 measurements from 46 sites, and is openly accessible through the PROMICE web portal (http://www.promice.dk). For each measurement we provide X, Y and Z coordinates, starting and ending dates as well as quality flags. We give sources for each entry and for all metadata. Two thirds of the data were collected from grey literature and unpublished archive documents. Roughly 60% of the measurements were performed by the Geological Survey of Denmark and Greenland (GEUS, previously GGU). The data cover all regions of Greenland except for the southernmost part of the east coast, but also emphasize the importance of long-term time series of which there are only two exceeding 20 a. We use the data to analyse uncertainties in point measurements of surface mass balance, as well as to estimate surface mass-balance profiles for most regions of Greenland.

We present a preliminary analysis of the self-absorbed [CII]-spectra observed with SOFIA/GREAT towards NGC 2024. Together with the detected [13CII] hyperfine satellites, the observed spectra require surprisingly high column densities of C+, both in the warm core and the foreground absorption component. Such high column densities are a challenge to explain with present state-of-the-art PDR models of the UV/molecular cloud interaction.

Cellular cholesterol homeostasis is a fundamental and highly regulated process. Transcription factors known as sterol regulatory element binding proteins (SREBPs) coordinate the expression of many genes involved in the biosynthesis and uptake of cholesterol. Dysregulation of SREBP activation and cellular lipid accumulation has been associated with endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR). This review will provide an overview of ER stress and the UPR as well as cholesterol homeostasis and SREBP regulation, with an emphasis on their interaction and biological relevance.

We observed several H ii regions in the dwarf irregular galaxy NGC 6822 using the infrared spectrograph on the Spitzer Space Telescope. Our aim is twofold: first, to examine the neon to sulfur abundance ratio in order to determine how much it may vary and whether or not, it is fairly ‘universal’; second, to discriminate and test the predicted ionizing spectral energy distribution between various stellar atmosphere models by comparing with our derivation of the ratio of fractional ionizations involving neon and sulfur. This work extends our previous similar studies of H ii regions in M83 and M33 to lower metallicities.

The ARGOS Food and Dose Module has been adopted by the RPII to simulate the transfer of radioactivity in the food chain in the event of a large scale nuclear incident and to enhance its capability to assess the radiological consequences. This paper describes adaptation of this model for Irish conditions and its intended use, illustrated with examples from a recent national emergency exercise. By enabling time series of activity concentrations of individual radionuclide or radionuclide groups in a range of food and animal feeds and comparison with appropriate action levels, the model would assist the formulation of early advice regarding countermeasures and would be an important factor in refining a pre-defined sampling strategy. The current implementation provides a basis for more detailed modelling which would inevitably be required in the event of a real incident. As the situation evolved and monitoring results became available, FDM could be refined and used to predict future concentrations or those over a wide spatial area with increased confidence.

The Radiological Protection Institute of Ireland (RPII) monitors airborne radioactivity concentrations at ten stations throughout Ireland, of which nine are equipped with low volume particulate samplers and one, in Dublin, with a high volume particulate sampler. The low volume particulate samples are assessed for total beta activity. In the period 1998-2003 the total beta activity concentrations observed have been consistently low, ranging between 0.03 and 1.33 mBq m-3 with a mean over all sampling sites of 0.26 ± 0.15 mBq m-3 (n = 2361). High volume particulate samples have been assessed for caesium-137 and beryllium-7. A mean caesium-137 activity concentration of 2.3 ± 2.2 mBq m-3 (n = 26) was observed in samples taken since 1993 while the mean beryllium-7 activity concentration over this period was 3.0 ± 1.6 mBq m-3 (n = 42). In addition, air sampled at the RPII's laboratory in Dublin, is monitored for krypton-85, a radioactive noble gas, released into the environment primarily as a result of the reprocessing of nuclear fuel at installations such as Sellafield in the UK and Cogema La Hague in France. Analysis of the krypton-85 monitoring data, along with additional backward air trajectory modelling, demonstrate the influence of the reprocessing plants on the krypton-85 concentrations in Ireland. 


Background. Evidence suggests that schizophrenia may be a disorder with origins in early intrauterine mal-development. We have constructed a comprehensive anthropometric scale for the evaluation of dysmorphic features as an index of the nature and timing of developmental disturbance.

Method. A detailed set of craniofacial and bodily measures was compiled and applied to 174 patients with schizophrenia and 80 matched control subjects.

Results. Patients had significantly higher scores on this scale and displayed multiple anomalies of the craniofacial region with an overall narrowing and elongation of the mid-face and lower face. Twelve craniofacial anomalies independently distinguished patients from controls and these variables correctly classified 95% of patients and 80% of control subjects.

Conclusions. This new scale, while procedurally more exacting than the Waldrop scale, more clearly defines the topography of anomalies previously suspected in individuals with schizophrenia. These findings constitute direct evidence for disturbed craniofacial development in schizophrenia and indicate origins in the foetal period during which the characteristic human facial pattern evolves in close association with brain differentiation.

The interdiffusion of Cu and Sn and the formation and dissolution of Cu-Sn precipitate phases have been examined for Cu(Sn) alloy thin films. Cu(Sn) films were deposited by electron beam evaporation in either a Sn/Cu bilayer or Cu/Sn/Cu trilayer film structure, with overall Sn concentrations from 0.1 to 5 atomic percent. Analysis by in situ resistivity, calorimetry, electron diffraction and x-ray diffraction measurements indicates that the bilayer and trilayer films form the intermetallic phase η-Cu6 Sn5 during film deposition. Upon heating, the ε-Cu3Sn phase forms at 170°C, then this phase dissolves into the Cu matrix at approximately 350°C. Finally, ζ- Cu10Sn3 phase forms and precipitates after heating to 500°C and cooling to room temperature. The final resistivity of Cu/Sn/Cu films with more than 2 atomic percent Sn was greater than 3.5 μΩ - cm. However, resistivities from 1.9 to 2.5 μΩ - cm after annealing were obtained with Cu/Sn/Cu films containing less than 2 atomic percent Sn.

Measurement of resistance in-situ during rapid thermal annealing is a powerful technique for process characterization and optimization. A major advantage of in-situ resistance measurements is the very rapid process learning. With silicides, in-situ resistance measurements can quickly determine an appropriate thermal process in which a low resistance silicide phase is formed without the agglomeration or inversion of silicide/polycrystalline silicon structures. One example is an optimized two step anneal for CoSi2 formation which was developed in less than one day. Examples of process characterization include determining the phase formation kinetics of TiSi2 (C49 and C54), Co2Si, and CoSi2 using in-situ ramped resistance measurements. The stability of TiSi2 or CoSi2/poly-Si structures has also been characterized by isothermal measurements. Resistance measurements have been made at heating rates from 1 to 100°C/s and temperatures up to 1000°C. The sample temperature was calibrated by melting Ag, Al, or Au/Si eutectics.

Measurement of resistance in-situ during rapid thermal annealing is a powerful technique for process characterization and optimization. A major advantage of in-situ resistance measurements is the very rapid process learning. With silicides, in-situ resistance measurements can quickly determine an appropriate thermal process in which a low resistance silicide phase is formed without the agglomeration or inversion of silicide/polycrystalline silicon structures. One example is an optimized two step anneal for CoSi2 formation which was developed in less than one clay. Examples of process characterization include determining the phase formation kinetics of TiSi2 (C49 and C54), Co2Si, and CoSi2 using in-situ ramped resistance measurements. The stability of TiSi2 or CoSi2/poly-Si structures has also been characterized by isothermal measurements. Resistance measurements have been made at heating rates from 1 to 100°C/s and temperatures up to 1000°C. The sample temperature was calibrated by melting Ag, Al, or Au/Si eutectics.

Significant progress has been made in building multilevel copper interconnection systems for advanced microelectronics. In this article, we examine some of the materials science issues underlying this progress, and indicate where significant materials challenges remain. It is probable that several approaches to process integration will be developed for copper interconnections, as has been the case with aluminum systems. The first successful demonstration of a fully integrated 4-level copper/polyimide (Cu/PI) interconnection system has been described by Luther et al. of IBM. A schematic cross section of this interconnection system is shown in Figure 1, indicating multiple layers of BPDA-PDA polyimide (PI 5810), Cu lines and studs, and layers of Ta and Si3N4 which serve as diffusion barriers, adhesion layers, and stopping layers in the patterning and planarization processes. This system demonstrates excellent planarity, as shown in the SEM cross section in Figure 2. The electromigration lifetime of this Cu/PI system is greatly improved relative to state-of-the-art aluminum-based systems, and the dielectric integrity appears adequate. Signal propagation studies also confirm the performance improvements anticipated for copper as a low-resistivity conductor and the use of Cu may allow significant capacitance reduction (≃ 25%) simply by scaling Cu lines to equal the resistance of Al lines. In parallel with efforts to introduce Cu metallization for its low resistivity, extensive efforts are under way to replace SiO2 with lower dielectric constant insulators.

Interconnections on silicon-based integrated circuits are almost exclusively aluminum alloys (Al-Si, Cu and various other solutes, e.g., Pd, Sc). The effects of film microstructure (grain size, grain size distribution, crystallographic texture and precipitate distribution) on the reliability of single level Al metallization has been well established. The final film microstructure obtained is dependent on both the deposition conditions and the thermal history during the manufacturing process. This paper will consider the role of microstructure in multi-level interconnects consisting of (1) AI(Cu) lines (in SiO2) with W and/or AI(Cu) studs and (2) an all Cu/polyimide multi-level structure. Methods for microstructure optimization during manufacturing of both Al and Cu based multilevel structures are explored. The variables important in determining the reliability of submicrometer single level versus multi-level structures and reliability testing methods (e.g., samples with versus without reservoirs and wafer level techniques) will be reviewed. Two relevant questions raised are; (1) What can be done during manufacturing to "build-in" reliability?, and (2) What are the trade-offs between manufacturing complexity (i.e., cost) and inherent reliability?

We describe an approach for rapid evaluation of thin film interfacial reactions using a combination of temperature-ramped in situ measurements of sheet resistance, calorimetry and stress. Electrical, mechanical and thermal measurements at elevated temperatures provide detailed reaction information which is unavailable in room temperature measurements. Kinetic data is particularly useful in making comparisons with mechanistic models. The following examples are discussed:

1. Effects of interfacial oxygen on Ta as a diffusion barrier between Cu and Si,

2. Effects of interfacial oxygen on the Cu/Mg reaction to form CuMg2 and Cu2Mg,

3. Effects of the density of internal interfaces (grain boundaries) on Al2Cu dissolution and precipitation in Al-Cu alloys.

Aluminum films 1–6 kÅ thick deposited on Pt or Pd layers developed voids after annealing between 200 and 275°C. Void formation was also observed when the Pt layer was deposited above the Al film. The amount of Al surrounding the voids increased as the voids grew. The rate of void growth decreased as the thickness of the initial Al film increased. The driving force appears to be surface tension. The controlling mechanism is diffusion along the Al/Pt or Al/Pd interface made possible by compound formation there.

Using a planar thin-film specimen geometry, the growth kinetics of the spinel in NiOAl2O3 system has been studied with Rutherford backscattering spectroscopy. A thin-layer of Ni film is deposited by the electron-beam deposition technique onto single-crystal alumina substrates of different orientations including, (0001), {1120}, {1102} and {1100}. The subsequent heat-treatment in air then converts the Ni to NiO, thus producing a uniform layer of NiO with good adhesion between the NiO and the alumina. The kinetics of the Ni-Al spinel growth has been found to be different for different single-crystal substrate orientations. The kinetics behavior follows a parabolic growth-rate law for each orientation but shows a different reaction-rate constant. X-ray diffraction and transmission electron microscopy have been used as complementary techniques to confirm the phases that form at each stage of the heat treatment and the corresponding microstructures of the thin-film layers respectively.