Up to now, state‐of‐the‐art empirical slant delay modeling for processing observations from radio space geodetic techniques has been provided by a combination of two empirical models. These are GPT ...(Global Pressure and Temperature) and GMF (Global Mapping Function), both operating on the basis of long‐term averages of surface values from numerical weather models. Weaknesses in GPT/GMF, specifically their limited spatial and temporal variability, are largely eradicated by a new, combined model GPT2, which provides pressure, temperature, lapse rate, water vapor pressure, and mapping function coefficients at any site, resting upon a global 5° grid of mean values, annual, and semi‐annual variations in all parameters. Built on ERA‐Interim data, GPT2 brings forth improved empirical slant delays for geophysical studies. Compared to GPT/GMF, GPT2 yields a 40% reduction of annual and semi‐annual amplitude differences in station heights with respect to a solution based on instantaneous local pressure values and the Vienna mapping functions 1, as shown with a series of global VLBI (Very Long Baseline Interferometry) solutions.
Key Points
Refined tropospheric delay model based on ERA‐Interim
Excellent match of empirical model pressure to in‐situ pressure values
Improved station height estimates deduced from VLBI observations
A new realization of the International Celestial Reference Frame (ICRF) is presented based on the work achieved by a working group of the International Astronomical Union (IAU) mandated for this ...purpose. This new realization follows the initial realization of the ICRF completed in 1997 and its successor, ICRF2, adopted as a replacement in 2009. The new frame, referred to as ICRF3, is based on nearly 40 years of data acquired by very long baseline interferometry at the standard geodetic and astrometric radio frequencies (8.4 and 2.3 GHz), supplemented with data collected at higher radio frequencies (24 GHz and dual-frequency 32 and 8.4 GHz) over the past 15 years. State-of-the-art astronomical and geophysical modeling has been used to analyze these data and derive source positions. The modeling integrates, for the first time, the effect of the galactocentric acceleration of the solar system (directly estimated from the data) which, if not considered, induces significant deformation of the frame due to the data span. The new frame includes positions at 8.4 GHz for 4536 extragalactic sources. Of these, 303 sources, uniformly distributed on the sky, are identified as “defining sources” and as such serve to define the axes of the frame. Positions at 8.4 GHz are supplemented with positions at 24 GHz for 824 sources and at 32 GHz for 678 sources. In all, ICRF3 comprises 4588 sources, with three-frequency positions available for 600 of these. Source positions have been determined independently at each of the frequencies in order to preserve the underlying astrophysical content behind such positions. They are reported for epoch 2015.0 and must be propagated for observations at other epochs for the most accurate needs, accounting for the acceleration toward the Galactic center, which results in a dipolar proper motion field of amplitude 0.0058 milliarcsecond yr
−1
(mas yr
−1
). The frame is aligned onto the International Celestial Reference System to within the accuracy of ICRF2 and shows a median positional uncertainty of about 0.1 mas in right ascension and 0.2 mas in declination, with a noise floor of 0.03 mas in the individual source coordinates. A subset of 500 sources is found to have extremely accurate positions, in the range of 0.03–0.06 mas, at the traditional 8.4 GHz frequency. Comparing ICRF3 with the recently released
Gaia
Celestial Reference Frame 2 in the optical domain, there is no evidence for deformations larger than 0.03 mas between the two frames, in agreement with the ICRF3 noise level. Significant positional offsets between the three ICRF3 frequencies are detected for about 5% of the sources. Moreover, a notable fraction (22%) of the sources shows optical and radio positions that are significantly offset. There are indications that these positional offsets may be the manifestation of extended source structures. This third realization of the ICRF was adopted by the IAU at its 30th General Assembly in August 2018 and replaced the previous realization, ICRF2, on January 1, 2019.
Radioactive ion beam facilities are transforming nuclear science by making beams of exotic nuclei with various properties available for experiments. New infrastructures and development of existing ...installations enlarges the scientific scope continuously. An overview of the main production, separation and beam handling methods with focus on recent developments is done, as well as a survey of existing and forthcoming facilities world-wide.
The Facility for Antiproton and Ion Research (FAIR) will be the accelerator-based flagship research facility in many basic sciences and their applications in Europe for the coming decades. FAIR will ...open up unprecedented research opportunities in hadron and nuclear physics, in atomic physics and nuclear astrophysics as well as in applied sciences like materials research, plasma physics and radiation biophysics with applications towards novel medical treatments and space science. FAIR is currently under construction as an international facility at the campus of the GSI Helmholtzzentrum for Heavy-Ion Research in Darmstadt, Germany. While the full science potential of FAIR can only be harvested once the new suite of accelerators and storage rings is completed and operational, some of the experimental detectors and instrumentation are already available and will be used starting in summer 2018 in a dedicated research program at GSI, exploiting also the significantly upgraded GSI accelerator chain. The current manuscript summarizes how FAIR will advance our knowledge in various research fields ranging from a deeper understanding of the fundamental interactions and symmetries in nature to a better understanding of the evolution of the Universe and the objects within.
We have used 10 years of ground‐based data from the Global Positioning System (GPS) to estimate time series of the excess propagation path due to the gases in the neutral atmosphere. We first derive ...the excess path caused by water vapor which in turn is used to infer the water vapor content above each one of 33 GPS receiver sites in Finland and Sweden. Although a 10 year period is much too short to search for climate change we use the data set to assess the stability and consistency of the linear trend of the water vapor content that can be estimated from the data. The linear trends in the integrated water vapor content range from −0.2 to +1.0 kg m−2 decade−1. As one may expect we find different systematic patterns for summer and winter data. The formal uncertainty of these trends, taking the temporal correlation of the variability about the estimated model into account, are of the order of 0.4 kg m−2 decade−1. Mostly, this uncertainty is due to the natural short‐term variability in the water vapor content, while the formal uncertainties in the GPS measurements have only a small impact on the trend errors.
A metal thermoelectric energy harvester design with long metal couples was investigated for use with wireless sensors in environments where conventional thermoelectric harvesters are difficult to ...implement. Two thermoelectric harvesters with different designs was assembled by spot welding 110 m thick molybdenum foil and 150 m thick nickel foil together in a zigzag-pattern, one 3-couples design (55 mm length and 6 mm width) insulated with glass fiber at the hot side and polyimide tape at the cold side, and one 10-couples design (300 mm length and 3 mm width) insulated with polyimide tape across the entire length. The voltage- and power output were measured at different temperatures and load resistance with maximum power output of 588 W at 269 °C for the 3-couples harvester and 868 W at 241 °C for the 10-couples harvester. The power output after power management electronics for the 10-couples harvester measured 290 W at 51 mV. The harvesters were compared to a conventional semiconductor thermoelectric device coupled with a 300 mm long copper heat bridge giving a power output after power management electronics of 170 W at 41 mV with 226 °C temperature gradient of the environment.
Abstract
Objectives
Very early-life conditions are recognized as critical for healthy brain development. This study assesses early-life risk factors for developing dementia. In the absence of ...historical medical birth records, we leverage an alternative full population approach using demographic characteristics obtained from administrative data to derive proxy indicators for birth complications and unfavorable birth outcomes. We use proxy variables to investigate the impact of early-life risk factors on dementia risk.
Methods
We use administrative individual-level data for full cohorts born 1932–1950 in Sweden with multigenerational linkages. Records on hospitalization and mortality are used to identify dementia cases. We derive 3 birth risk factors based on demographic characteristics: advanced maternal age, narrow sibling spacing, and twin births, and apply survival analysis to evaluate long-term effects on dementia risk. We control for confounding using multiple indicators for socio-economic status (SES), including parental surnames, and by implementing a sibling design. As comparison exposure, we add low education from the 1970 Census.
Results
The presence of at least 1 birth risk factor increases dementia risk (HR = 1.059; 95% CI: 1.034, 1.085). The occurrence of twin births poses a particularly heightened risk (HR = 1.166; 95% CI: 1.084, 1.255).
Discussion
Improvements to the very early-life environment hold significant potential to mitigate dementia risk. A comparison to the influence of low education on dementia (the largest known modifiable risk factor) suggests that demographic birth characteristics are of relevant effect sizes. Our findings underscore the relevance of providing assistance for births experiencing complications and adverse health outcomes to reduce dementia cases.
Purpose
In the 30 years since the Stockholm Workshop Scale (SWS) was published, the scientific literature on hand–arm vibration syndrome (HAVS) has grown and experience has been gained in its ...practical application. This research was undertaken to develop an up-to-date evidence-based classification for HAVS by seeking consensus between experts in the field.
Methods
Seven occupational physicians who are clinically active and have had work published on HAVS in the last 10 years were asked to independently take part in a three-round iterative Delphi process. Consensus was taken when 5/7 (72%) agreed with a particular statement. Experts were asked to provide evidence from the literature or data from their own research to support their views.
Results
Consensus was achieved for most of the questions that were used to develop an updated staging system for HAVS. The vascular and neurological components from the SWS are retained, but ambiguous descriptors and tests without adequately developed methodology such as tactile discrimination, or discriminating power such as grip strength, are not included in the new staging system. A blanching score taken from photographs of the hands during vasospastic episodes is recommended in place of self-recall and frequency of attacks to stage vascular HAVS. Methods with the best evidence base are described for assessing sensory perception and dexterity.
Conclusions
A new classification has been developed with three stages for the clinical classification of vascular and neurological HAVS based on international consensus. We recommend it replaces the SWS for clinical and research purposes.
In urban environments, airborne particles are continuously emitted, followed by atmospheric aging. Also, particles emitted elsewhere, transported by winds, contribute to the urban aerosol. We studied ...the effective density (mass-mobility relationship) and mixing state with respect to the density of particles in central Copenhagen, in wintertime. The results are related to particle origin, morphology, and aging. Using a differential mobility analyzer-aerosol particle mass analyzer (DMA-APM), we determined that particles in the diameter range of 50–400 nm were of two groups: porous soot aggregates and more dense particles. Both groups were present at each size in varying proportions. Two types of temporal variability in the relative number fraction of the two groups were found: soot correlated with intense traffic in a diel pattern and dense particles increased during episodes with long-range transport from polluted continental areas. The effective density of each group was relatively stable over time, especially of the soot aggregates, which had effective densities similar to those observed in laboratory studies of fresh diesel exhaust emissions. When heated to 300 °C, the soot aggregate volatile mass fraction was ∼10%. For the dense particles, the volatile mass fraction varied from ∼80% to nearly 100%.
We assess the impact of atmospheric turbulence on geodetic very long baseline interferometry (VLBI) through simulations of atmospheric delays. VLBI observations are simulated for the two best ...existing VLBI data sets: The continuous VLBI campaigns CONT05 and CONT08. We test different methods to determine the magnitude of the turbulence above each VLBI station, i.e., the refractive index structure constant Cn2. The results from the analysis of the simulated data and the actually observed VLBI data are compared. We find that atmospheric turbulence today is the largest error source for geodetic VLBI. Accurate modeling of atmospheric turbulence is necessary to reach the highest accuracy with geodetic VLBI.
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