| 1. |
- Surendran, Praveen, et al.
(författare)
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Discovery of rare variants associated with blood pressure regulation through meta-analysis of 1.3 million individuals
- 2020
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Ingår i: Nature Genetics. - : Nature Publishing Group. - 1061-4036 .- 1546-1718. ; 52:12, s. 1314-1332
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Tidskriftsartikel (refereegranskat)abstract
- Genetic studies of blood pressure (BP) to date have mainly analyzed common variants (minor allele frequency > 0.05). In a meta-analysis of up to similar to 1.3 million participants, we discovered 106 new BP-associated genomic regions and 87 rare (minor allele frequency <= 0.01) variant BP associations (P < 5 x 10(-8)), of which 32 were in new BP-associated loci and 55 were independent BP-associated single-nucleotide variants within known BP-associated regions. Average effects of rare variants (44% coding) were similar to 8 times larger than common variant effects and indicate potential candidate causal genes at new and known loci (for example, GATA5 and PLCB3). BP-associated variants (including rare and common) were enriched in regions of active chromatin in fetal tissues, potentially linking fetal development with BP regulation in later life. Multivariable Mendelian randomization suggested possible inverse effects of elevated systolic and diastolic BP on large artery stroke. Our study demonstrates the utility of rare-variant analyses for identifying candidate genes and the results highlight potential therapeutic targets.
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| 2. |
- Alizadeh Khameneh, Mohammad Amin, 1983-
(författare)
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Optimal Design in Geodetic GNSS-based Networks
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An optimal design of a geodetic network helps the surveying engineers maximise the efficiency of the network. A number of pre-defined quality requirements, i.e. precision, reliability, and cost, of the network are fulfilled by performing an optimisation procedure. Today, this is almost always accomplished by implementing analytical solutions, where the human intervention in the process cycle is limited to defining the requirements. Nevertheless, a trial and error method can be beneficial to some applications. In order to analytically solve an optimisation problem, it can be classified to different orders, where an optimal datum, configuration, and optimal observation weights can be sought such that the precision, reliability and cost criteria are satisfied.In this thesis, which is a compilation of six peer-reviewed papers, we optimised and redesigned a number of GNSS-based monitoring networks in Sweden by developing new methodologies. In addition, optimal design and efficiency of total station establishment with RTK-GNSS is investigated in this research.Sensitivity of a network in detecting displacements is of importance for monitoring purposes. In the first paper, a precision criterion was defined to enable a GNSS-based monitoring network to detect 5 mm displacements at each network point. Developing an optimisation model by considering this precision criterion, reliability and cost yielded a decrease of 17% in the number of observed single baselines implying a reliable and precise network at lower cost. The second paper concerned a case, where the precision of observations could be improved in forthcoming measurements. Thus a new precision criterion was developed to consider this assumption. A significant change was seen in the optimised design of the network for subsequent measurements. As yet, the weight of single baselines was subject to optimisation, while in the third paper, the effect of mathematical correlations between GNSS baselines was considered in the optimisation. Hence, the sessions of observations, including more than two receivers, were optimised. Four out of ten sessions with three simultaneous operating receivers were eliminated in a monitoring network with designed displacement detection of 5 mm. The sixth paper was the last one dealing with optimisation of GNSS networks. The area of interest was divided into a number of three-dimensional elements and the precision of deformation parameters was used in developing a precision criterion. This criterion enabled the network to detect displacements of 3 mm at each point.A total station can be set up in the field by different methods, e.g. free station or setup over a known point. A real-time updated free station method uses RTK-GNSS to determine the coordinates and orientation of a total station. The efficiency of this method in height determination was investigated in the fourth paper. The research produced promising results suggesting using the method as an alternative to traditional levelling under some conditions. Moreover, an optimal location for the total station in free station establishment was studied in the fifth paper. It was numerically shown that the height component has no significant effect on the optimal localisation.
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| 3. |
- Håkansson, Martin, 1982-
(författare)
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Hardware biases and their impact on GNSS positioning
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- GNSS hardware biases appear in code and phase observations, and originates both from the receiver and satellite hardware. These biases influence the accuracy in precise GNSS positioning if not handled properly.This thesis is based on two papers, where one is a review paper published in GPS Solutions, and the other is a research paper currently in review (resubmitted after minor revision) for Journal of Geodetic Science. The first paper compiles current results and gives an overview of those situations where biases are of the greatest importance for precise positioning. The second paper investigates the satellite dependency in two cases of relative phase biases.In the first paper, a review is given on how hardware biases influence precise GNSS positioning in various situations. These can roughly be divided into five cases: positioning not employing the ionosphere free combination to which the satellite clock corrections are aligned, GNSS based ionospheric modeling, determination of the phase ambiguity as an integer in PPP, and positioning with GLONASS.In the second paper, the satellite dependency for two cases of relative phase biases are investigated: relative between-receiver biases in single differenced phase observations from two receivers, relative between-signals biases in observation differences between two signals recorded by the same receiver and associated with the same carrier frequency. In both these cases a satellite dependency was discovered. The first case showed a difference of 0.8 mm between the greatest and smallest values, while the corresponding difference in the second case was 3.5 mm.It was also discovered that the biases in the first case varied periodically over time, and with a period of one sidereal day. The exact cause for these variations could however not be determined in the experiment, even though multipath could be excluded as their source.
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| 4. |
- Alizadeh Khameneh, Mohammad Amin, et al.
(författare)
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Optimization of deformation monitoring networks using finite element strain analysis
- 2018
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Ingår i: Journal of Applied Geodesy. - : Walter de Gruyter GmbH. - 1862-9016 .- 1862-9024. ; 2:2, s. 187-197
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Tidskriftsartikel (refereegranskat)abstract
- An optimal design of a geodetic network can fulfill the requested precision and reliability of the network, and decrease the expenses of its execution by removing unnecessary observations. The role of an optimal design is highlighted in deformation monitoring network due to the repeatability of these networks. The core design problem is how to define precision and reliability criteria. This paper proposes a solution, where the precision criterion is defined based on the precision of deformation parameters, i. e. precision of strain and differential rotations. A strain analysis can be performed to obtain some information about the possible deformation of a deformable object. In this study, we split an area into a number of three-dimensional finite elements with the help of the Delaunay triangulation and performed the strain analysis on each element. According to the obtained precision of deformation parameters in each element, the precision criterion of displacement detection at each network point is then determined. The developed criterion is implemented to optimize the observations from the Global Positioning System (GPS) in Skåne monitoring network in Sweden. The network was established in 1989 and straddled the Tornquist zone, which is one of the most active faults in southern Sweden. The numerical results show that 17 out of all 21 possible GPS baseline observations are sufficient to detect minimum 3 mm displacement at each network point. © 2018 Walter de Gruyter GmbH, Berlin/Boston.
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| 5. |
- Håkansson, Martin, 1982-
(författare)
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GNSS hardware biases in code and carrier phase observables
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- GNSS hardware biases appear in code and phase observations, and originates both from the receiver and satellite hardware. The presence of biases in GNSS observations might affect the accuracy in precise GNSS positioning applications, and might also be of relevance in other GNSS applications. They may also be a cause of incompatibility between different receiver types or GNSS constellations.In this thesis, which is based on four papers, the biases in GNSS code and carrier phase observables are investigated. This is done by: characterizing and analyzing some selected biases; revealing some previously unknown biases; developing new methods to estimate some of the biases; and compiling and presenting information about biases in a new and comprehensive way.Paper 1 gives a full review of how various kinds of biases affect various applications of precise GNSS positioning, including multi-GNSS positioning and ambiguity resolved PPP.In Paper 2, two cases of relative phase biases, that potentially could degrade the positioning accuracy in precise positioning applications, are investigated. Fortunately, these biases turns out to be small in size with negligible effect on the positioning accuracy in both cases, which involves relative between-receivers biases for receivers of different type and between-signals biases for carrier phase observations of different signals associated with the same carrier frequency.Paper 3 characterizes GNSS observations from a Nexus 9 Android tablet. By doing this, it reveals a number of earlier unknown biases. A drift between the code and phase observable of -3 and 2 mm/s is revealed for GPS and GLONASS, respectively. Additionally, an unexpected variation in the GLONASS phase observable, which seems to be dependent on the topocentric range rate of the satellite, is discovered.In Paper 4, the existence of nadir dependent code biases is confirmed for GNSS observations from BeiDou-2 satellites of the BeiDou constellation by analyzing the residuals of 2-D and 3-D ionosphere modeling. This a new method to derive this kind of bias, independent of the earlier employed approach based on the multipath linear combination. The estimated effect is, however, too small to infer a similar nadir dependence for GPS and Galileo as well.
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