Browsing by Subject "INVERSION"

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  • Keronen, Petri; Reissell, Anni; Chevallier, Frederic; Siivola, Erkki; Pohja, Toivo; Hiltunen, Veijo; Hatakka, Juha; Aalto, Tuula; Rivier, Leonard; Ciais, Philippe; Jordan, Armin; Hari, Pertti; Viisanen, Yrjo; Vesala, Timo (2014)
  • Torppa, Johanna; Granvik, Mikael; Penttilä, Antti; Reitmaa, Jukka; Tudose, Violeta; Pelttari, Leena; Muinonen, Karri; Bakker, Jorgo; Navarro, Vicente; O’Mullane, William (2018)
    Abstract We present two added-value interfaces (AVIs) for analyzing photometric and spectroscopic data observed by the Gaia satellite. The Gaia Added-Value Interface for Temporal Analysis (GAVITEA) is used to calculate an estimate for the spin state and shape of an asteroid from its photometric data, and the Gaia Added-Value Interface for Spectral Classification (GAVISC) provides tools to define the taxonomic type and surface absorption coefficient based on spectroscopic asteroid data. Computations are mainly carried out using well-known methods of asteroid data analysis but the AVIs also offer the possibility to test novel methods that are specifically developed for analyzing temporally sparse photometric data, typical for Gaia.
  • Martikainen, J.; Muinonen, K.; Penttilä, A.; Cellino, A.; Wang, X. -B. (2021)
    Aims. We perform light curve inversion for 491 asteroids to retrieve phase curve parameters, rotation periods, pole longitudes and latitudes, and convex and triaxial ellipsoid shapes by using the sparse photometric observations from Gaia Data Release 2 and the dense ground-based observations from the DAMIT database. We develop a method for the derivation of reference absolute magnitudes and phase curves from the Gaia data, allowing for comparative studies involving hundreds of asteroids.Methods. For both general convex shapes and ellipsoid shapes, we computed least-squares solutions using either the Levenberg-Marquardt optimization algorithm or the Nelder-Mead downhill simplex method. Virtual observations were generated by adding Gaussian random errors to the observations, and, later on, a Markov chain Monte Carlo method was applied to sample the spin, shape, and scattering parameters. Absolute magnitude and phase curve retrieval was developed for the reference geometry of equatorial illumination and observations based on model magnitudes averaged over rotational phase.Results. The derived photometric slope values showed wide variations within each assumed Tholen class. The computed Gaia G-band absolute magnitudes matched notably well with the V-band absolute magnitudes retrieved from the Jet Propulsion Laboratory Small-Body Database. Finally, the reference phase curves were well fitted with the H, G(1), G(2) phase function. The resulting G(1), G(2) distribution differed, in an intriguing way, from the G(1), G(2) distribution that is based on the phase curves corresponding to light curve brightness maxima.
  • Koivula, Kimmo; Nikus, Kjell; Viikilä, Juho; Lilleberg, Jyrki; Huhtala, Heini; Birnbaum, Yochai; Eskola, Markku (2019)
    Background Both Q waves and T-wave inversion (TWI) in the presenting ECG are associated with a progressed stage of myocardial infarction, possibly with less potential for myocardial salvage with reperfusion therapy. Combining the diagnostic information from the Q- and T-wave analyses could improve the prognostic work-up in ST-elevation myocardial infarction (STEMI) patients. Methods We sought to determine the prognostic impact of Q waves and TWI in the admission ECG on patient outcome in STEMI. We formed four groups according to the presence of Q waves and/or TWI (Q+TWI+; Q-TWI+; Q+TWI-; Q-TWI-). We studied 627 all-comers with STEMI derived from two patient cohorts. Results The patients with Q+TWI+ had the highest and those with Q-TWI- the lowest 30-day and one-year mortality. One-year mortality was similar between Q-TWI+ and Q+TWI-. The survival analysis showed higher early mortality in Q+TWI- but the higher late mortality in Q-TWI+ compensated for the difference at 1 year. The highest peak troponin level was found in the patients with Q+TWI-. Conclusion Q waves and TWI predict adverse outcome, especially if both ECG features are present. Q waves and TWI predict similar one-year mortality. Extending the ECG analysis in STEMI patients to include both Q waves and TWI improves risk stratification.
  • Fung, Pak Lun; Zaidan, Martha Arbayani; Surakhi, Ola; Tarkoma, Sasu; Petäjä, Tuukka; Hussein, Tareq (2021)
    In air quality research, often only size-integrated particle mass concentrations as indicators of aerosol particles are considered. However, the mass concentrations do not provide sufficient information to convey the full story of fractionated size distribution, in which the particles of different diameters (Dp) are able to deposit differently on respiratory system and cause various harm. Aerosol size distribution measurements rely on a variety of techniques to classify the aerosol size and measure the size distribution. From the raw data the ambient size distribution is determined utilising a suite of inversion algorithms. However, the inversion problem is quite often ill-posed and challenging to solve. Due to the instrumental insufficiency and inversion limitations, imputation methods for fractionated particle size distribution are of great significance to fill the missing gaps or negative values. The study at hand involves a merged particle size distribution, from a scanning mobility particle sizer (NanoSMPS) and an optical particle sizer (OPS) covering the aerosol size distributions from 0.01 to 0.42 µm (electrical mobility equivalent size) and 0.3 to 10 µm (optical equivalent size) and meteorological parameters collected at an urban background region in Amman, Jordan, in the period of 1 August 2016–31 July 2017. We develop and evaluate feed-forward neural network (FFNN) approaches to estimate number concentrations at particular size bin with (1) meteorological parameters, (2) number concentration at other size bins and (3) both of the above as input variables. Two layers with 10–15 neurons are found to be the optimal option. Worse performance is observed at the lower edge (0.01<Dp<0.02 µm), the mid-range region (0.15<Dp<0.5 µm) and the upper edge (6<Dp<10 µm). For the edges at both ends, the number of neighbouring size bins is limited, and the detection efficiency by the corresponding instruments is lower compared to the other size bins. A distinct performance drop over the overlapping mid-range region is due to the deficiency of a merging algorithm. Another plausible reason for the poorer performance for finer particles is that they are more effectively removed from the atmosphere compared to the coarser particles so that the relationships between the input variables and the small particles are more dynamic. An observable overestimation is also found in the early morning for ultrafine particles followed by a distinct underestimation before midday. In the winter, due to a possible sensor drift and interference artefacts, the estimation performance is not as good as the other seasons. The FFNN approach by meteorological parameters using 5 min data (R2= 0.22–0.58) shows poorer results than data with longer time resolution (R2= 0.66–0.77). The FFNN approach using the number concentration at the other size bins can serve as an alternative way to replace negative numbers in the size distribution raw dataset thanks to its high accuracy and reliability (R2= 0.97–1). This negative-number filling approach can maintain a symmetric distribution of errors and complement the existing ill-posed built-in algorithm in particle sizer instruments.
  • Taylor, G.; Hillers, G. (2020)
    We present a new method for estimating time-series of relative seismic velocity changes (dv/v) within the Earth. Our approach is a Markov chain Monte Carlo (MCMC) technique that seeks to construct the full posterior probability distribution of the dv/v variations. Our method provides a robust, computationally efficient way to compute dv/v time-series that can incorporate information about measurement uncertainty, and any prior constraints that may be available. We demonstrate the method with a synthetic experiment, and then apply the MCMC algorithm to three data examples. In the first two examples we reproduce dv/v time-series associated with the response to the 2010 M 7.2 El Mayor-Cucapah earthquake at two sites in southern California, that have been studied in previous literature. In the San Jacinto fault zone environment we reproduce the dv/v signature of a deep creep slip sequence triggered by the El Mayor-Cucapah event, that is superimposed on a strong seasonal signal. At the Salton Sea Geothermal Field we corroborate the previously observed drop-and-recovery in seismic velocity caused by ground shaking related to the El Mayor-Cucapah event. In a third, new example we compute a month long velocity change time-series at hourly resolution at Pinion Flat, California. We observe a low amplitude variation in seismic velocity with a dominant frequency of 1 cycle per day, as well as a second transient signal with a frequency of 1.93 cycles per day. We attribute the 1-d periodicity in the dv/v variation to the combined effects of the diurnal tide and solar heating. The frequency of the signal at 1.93 cycles per day matches that of the lunar (semi-diurnal) tide. Analysis of the uncertainties in the Pinion Flat time-series shows that the error contains a signal with a frequency of 1 cycle per day. We attribute this variation to seismic noise produced by freight trains operating within the Coachella Valley. By demonstrating the applicability of the MCMC method in these examples, we show that it is well suited to tackle problems involving large data volumes that are typically associated with modern seismic experiments.
  • Bocci, Giuliano; Bianchi, Valentina; Cruschina, Silvio (2021)
    This paper addresses two long-standing issues concerning focus: first, the question of whether the focal interpretation is directly read off the prosodic structure of a sentence, or it is rather mediated by a [focus] feature encoded in the syntactic representation; second, whether interrogativewh-phrases are inherently endowed with a [focus] feature. We provide evidence from two prosodic experiments on directwh-questions in Italian, showing that the Nuclear Pitch Accent (NPA) and main stress fall on the lexical verb, without a concomitant focal interpretation of the latter. Furthermore, we show that NPA assignment is sensitive to the derivational history of thewh-phrase under short-distance vs. long-distance extraction. We account for the observed NPA distribution in terms of a [focus] feature which is bundled with the [wh] in direct questions, and is specified on each phase head that hosts in its edge one link of thewh-chain. Thus, v degrees is specified for the feature bundle {wh, focus} and attracts the assignment of the NPA, which is then realized on the lexical verb. Our findings, thus, cast doubt on the direct association between prosodic prominence and a focal interpretation.
  • Gaia Collaboration; Spoto, F.; Muinonen, K.; Granvik, M.; Fedorets, G.; Siltala, L. (2018)
    Context. The Gaia spacecraft of the European Space Agency (ESA) has been securing observations of solar system objects (SSOs) since the beginning of its operations. Data Release 2 (DR2) contains the observations of a selected sample of 14,099 SSOs. These asteroids have been already identified and have been numbered by the Minor Planet Center repository. Positions are provided for each Gaia observation at CCD level. As additional information, complementary to astrometry, the apparent brightness of SSOs in the unfiltered G band is also provided for selected observations. Aims. We explain the processing of SSO data, and describe the criteria we used to select the sample published in Gaia DR2. We then explore the data set to assess its quality. Methods. To exploit the main data product for the solar system in Gaia DR2, which is the epoch astrometry of asteroids, it is necessary to take into account the unusual properties of the uncertainty, as the position information is nearly one-dimensional. When this aspect is handled appropriately, an orbit fit can be obtained with post-fit residuals that are overall consistent with the a-priori error model that was used to define individual values of the astrometric uncertainty. The role of both random and systematic errors is described. The distribution of residuals allowed us to identify possible contaminants in the data set (such as stars). Photometry in the G band was compared to computed values from reference asteroid shapes and to the flux registered at the corresponding epochs by the red and blue photometers (RP and BP). Results. The overall astrometric performance is close to the expectations, with an optimal range of brightness G similar to 12 - 17. In this range, the typical transit-level accuracy is well below 1 mas. For fainter asteroids, the growing photon noise deteriorates the performance. Asteroids brighter than G similar to 12 are affected by a lower performance of the processing of their signals. The dramatic improvement brought by Gaia DR2 astrometry of SSOs is demonstrated by comparisons to the archive data and by preliminary tests on the detection of subtle non-gravitational effects.
  • Brander, Tommi; Ilmavirta, Joonas; Piiroinen, Petteri; Tyni, Teemu (2020)
    We study an inverse problem where an unknown radiating source is observed with collimated detectors along a single line and the medium has a known attenuation. The research is motivated by applications in SPECT and beam hardening. If measurements are carried out with frequencies ranging in an open set, we show that the source density is uniquely determined by these measurements up to averaging over levelsets of the integrated attenuation. This leads to a generalized Laplace transform. We also discuss some numerical approaches and demonstrate the results with several examples.
  • Cai, Runlong; Jiang, Jingkun; Mirme, Sander; Kangasluoma, Juha (2019)
    Measuring aerosol size distributions accurately down to similar to 1 nm is a key to nucleation studies, and it requires developments and improvements in instruments such as electrical mobility spectrometers in use today. The key factors characterizing the performance of an electrical mobility spectrometer for sub-3 nm particles are discussed in this study. A parameter named as Pi is proposed as a figure of merit for the performance of an electrical mobility spectrometer in the sub-3 nm size range instead of the overall detection efficiency. Pi includes the overall detection efficiency, the measurement time in each size bin, the aerosol flow rate passing through the detector, and the aerosol-to-sheath flow ratio of the differential mobility analyzer. The particle raw count number recorded by the detector can be estimated using Pi at a given aerosol size distribution function, dN/dlogd(p)( ). The limit of detection for the spectrometer and the statistical uncertainty of the measured aerosol size distribution can also be readily estimated using Pi. In addition to Pi, the size resolution of an electrical mobility analyzer is another factor characterizing the systematic errors originated from particle sizing. Four existing electrical mobility spectrometers designed for measuring sub-3 nm aerosol size distributions, including three scanning/differential mobility particle spectrometers and one differential mobility analyzer train, are examined. Their optimal performance is evaluated using Pi and the size resolution. For example, the Pi value and the size resolution of a diethylene-glycol differential mobility particle spectrometer for 1.5 nm particles are 8.0 x 10(-4) cm(3) and 5.7, respectively. The corresponding relative uncertainty of the measured size distribution is approximately 9.6% during an atmospheric new particle formation event with a dN/dlogd(p) of 5 x 10(5) cm(-3) . Assuming an adjustable sheath flow rate of the differential mobility analyzer, the optimal size resolution is approximately 5-9 when measuring atmospheric new particle formation events.
  • Holkeri, Arttu; Eranti, Antti; Haukilahti, M. Anette; Kerola, Tuomas; Kenttä, Tuomas; Noponen, Kai; Seppänen, Tapio; Rissanen, Harri; Heliövaara, Markku; Knekt, Paul; Junttila, M. Juhani; Huikuri, Heikki V.; Aro, Aapo L. (2019)
    Negative U-waves are a relatively rare finding in an electrocardiogram (ECG), but are often associated with cardiac disease. The prognostic significance of negative U-waves in the general population is unknown. We evaluated 12-lead ECGs of 6,518 adults (45% male, mean age 50.9 +/- 13.8 years) for the presence of U-waves, and followed the subjects for 24.5 +/- 10.3 years. Primary end points were all-cause mortality, cardiac mortality, and sudden cardiac death; secondary end point was hospitalization due to cardiac causes. Negative U-waves (amplitude >= 0.05 mV) were present in 231 subjects (3.5%), minor negative (amplitude <0.05 mV) or discordant U-waves in 1,004 subjects (15.4%), normal positive U-waves in 3,950 (60.6%) subjects, and no U-waves were observed in 603 subjects (9.3%). In 730 subjects (11.2%), U-waves were unassessable. When adjusted for age and gender, negative U-waves were associated with all end points (p <0.01). In an analysis adjusted for multiple demographic and clinical factors, in men, negative U-waves were associated with increased risk of all-cause mortality (hazard ratio [HR] 1.60; 95% confidence interval [CI] 1.26 to 2.03; p <0.001), cardiac mortality (HR 1.74; 95% CI 1.26 to 2.39; p = 0.001), and cardiac hospitalization (HR 1.67; 95% CI 1.27 to 2.18; p <0.001), but not with sudden cardiac death, whereas women did not show a significant association to any of the end points (p > 0.30). In conclusion, negative U-waves are associated with adverse events in the general population. In men, this association is independent of cardiovascular risk factors. (C) 2018 Elsevier Inc. All rights reserved.
  • Muukkonen, Ilkka; Ölander, Kaisu; Numminen, Jussi Kustaa; Salmela, Viljami (2020)
    The temporal and spatial neural processing of faces has been investigated rigorously, but few studies have unified these dimensions to reveal the spatio-temporal dynamics postulated by the models of face processing. We used support vector machine decoding and representational similarity analysis to combine information from different locations (fMRI), time windows (EEG), and theoretical models. By correlating representational dissimilarity matrices (RDMs) derived from multiple pairwise classifications of neural responses to different facial expressions (neutral, happy, fearful, angry), we found early EEG time windows (starting around 130 ​ms) to match fMRI data from primary visual cortex (V1), and later time windows (starting around 190 ​ms) to match data from lateral occipital, fusiform face complex, and temporal-parietal-occipital junction (TPOJ). According to model comparisons, the EEG classification results were based more on low-level visual features than expression intensities or categories. In fMRI, the model comparisons revealed change along the processing hierarchy, from low-level visual feature coding in V1 to coding of intensity of expressions in the right TPOJ. The results highlight the importance of a multimodal approach for understanding the functional roles of different brain regions in face processing.
  • Roedenbeck, C.; Zaehle, S.; Keeling, R.; Heimann, M. (2020)
    In 2018, central and northern parts of Europe experienced heat and drought conditions over many months from spring to autumn, strongly affecting both natural ecosystems and crops. Besides their impact on nature and society, events like this can be used to study the impact of climate variations on the terrestrial carbon cycle, which is an important determinant of the future climate trajectory. Here, variations in the regional net ecosystem exchange (NEE) of CO(2)between terrestrial ecosystems and the atmosphere were quantified from measurements of atmospheric CO(2)mole fractions. Over Europe, several observational records have been maintained since at least 1999, giving us the opportunity to assess the 2018 anomaly in the context of at least two decades of variations, including the strong climate anomaly in 2003. In addition to an atmospheric inversion with temporally explicitly estimated anomalies, we use an inversion based on empirical statistical relations between anomalies in the local NEE and anomalies in local climate conditions. For our analysis period 1999-2018, we find that higher-than-usual NEE in hot and dry summers may tend to arise in Central Europe from enhanced ecosystem respiration due to the elevated temperatures, and in Southern Europe from reduced photosynthesis due to the reduced water availability. Despite concerns in the literature, the level of agreement between regression-based NEE anomalies and temporally explicitly estimated anomalies indicates that the atmospheric CO(2)measurements from the relatively dense European station network do provide information about the year-to-year variations of Europe's carbon sources and sinks, at least in summer. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.