| 11. |
- Almquist, Martin, et al.
(författare)
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Atmospheric Sound Propagation Over Large-Scale Irregular Terrain
- 2014
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Ingår i: Journal of Scientific Computing. - : Springer Science and Business Media LLC. - 0885-7474 .- 1573-7691. ; 61:2, s. 369-397
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Tidskriftsartikel (refereegranskat)abstract
- A benchmark problem on atmospheric sound propagation over irregular terrain has been solved using a stable fourth-order accurate finite difference approximation of a high-fidelity acoustic model. A comparison with the parabolic equation method and ray tracing methods is made. The results show that ray tracing methods can potentially be unreliable in the presence of irregular terrain.
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| 12. |
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| 13. |
- Almquist, Martin
(författare)
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Calcium metabolism and breast cancer risk
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Emerging evidence suggests that calcium and its regulating hormones, i.e. vitamin D and parathyroid hormone (PTH), affect breast cancer risk. The associations between serum calcium levels and breast cancer risk, between serum calcium levels and known risk factors of breast cancer, and between serum calcium levels and breast cancer aggressiveness were examined within the Malmö Preventive Project, a population-based cohort comprising 10,902 women. Serum calcium, 25-hydroxyvitamin D (25OHD) and PTH-levels were furthermore examined in relation to breast cancer risk in a nested case-control study comprising 764 breast cancer cases within the Malmö Diet and Cancer Study. Serum calcium levels were positively associated with breast cancer risk in overweight/obese women. In premenopausal women, serum calcium was in one study negatively, and in one study positively, associated with breast cancer. Calcium was positively associated with breast cancer aggressiveness in overweight and/or premenopausal women. Premenopausal status and use of oral contraceptives and hormone-replacement therapy were negatively associated with serum calcium levels. BMI was significantly associated with serum calcium levels, with lean and overweight women having higher calcium levels than women with BMI between 20 and 25. There was a weak, statistically non-significant, inverse association between 25OHD-levels and breast cancer risk. There was no evidence for any relation between PTH-levels and breast cancer. It is concluded that serum calcium is positively associated with breast cancer risk and aggressiveness in overweight women. There may be a weak negative association between vitamin D and breast cancer risk, but this will have to be further examined.
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| 14. |
- Almquist, Martin, et al.
(författare)
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Cardiac arrest with vagal stimulation during intraoperative nerve monitoring.
- 2016
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Ingår i: Head and Neck. - : Wiley. - 1043-3074.
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Tidskriftsartikel (refereegranskat)abstract
- Intraoperative neuromonitoring (IONM) is widely used during thyroid surgery. During both intermittent and continuous IONM stimulation of the vagus nerve is performed. This has previously been reported to be safe.
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| 15. |
- Almquist, Martin, et al.
(författare)
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Changing biochemical presentation of primary hyperparathyroidism.
- 2010
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Ingår i: Langenbeck's Archives of Surgery. - : Springer Science and Business Media LLC. - 1435-2451 .- 1435-2443. ; 395, s. 925-928
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: Patients with primary hyperparathyroidism, pHPT, present with milder symptoms than previously. Some, but not all studies, suggest that this change in clinical pattern also implies lower preoperative parathyroid hormone (PTH) and/or calcium levels and smaller adenomas. This is important since reports indicate that smaller adenomas are more difficult to detect on preoperative imaging, possibly increasing the risk of surgical failure. METHODS: There were 640 patients with histologically confirmed single-gland pHPT identified in a prospectively collected database. Median values of preoperative calcium, PTH, as well as adenoma weight were compared in three different time periods: 1990-1995, 1996-2000, and 2000-2007. Correlation between the preoperative levels of calcium and PTH and adenoma weight was calculated. RESULTS: Preoperative ionized calcium decreased significantly over time (p < 0.001). There was a positive correlation between preoperative PTH and adenoma weight (r = 0.32, p < 0.001). The magnitude of this correlation decreased over time. In women, adenoma weight decreased significantly over time (p = 0.03). Median (25th-75th percentile) adenoma weight in women was 750 (400-1,380) mg, 650 (350-1,205) mg, and 520 (305-1,065) mg in the first, second, and third period, respectively. CONCLUSION: From 1990 to 2007, there was a significant trend to operate pHPT patients with lower preoperative serum ionized calcium levels. In women, the adenoma weight decreased. This trend could potentially lead to decreased sensitivity in preoperative localization procedures.
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| 16. |
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| 17. |
- Almquist, Martin, 1988-
(författare)
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Efficient Simulation of Wave Phenomena
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wave phenomena appear in many fields of science such as acoustics, geophysics, and quantum mechanics. They can often be described by partial differential equations (PDEs). As PDEs typically are too difficult to solve by hand, the only option is to compute approximate solutions by implementing numerical methods on computers. Ideally, the numerical methods should produce accurate solutions at low computational cost. For wave propagation problems, high-order finite difference methods are known to be computationally cheap, but historically it has been difficult to construct stable methods. Thus, they have not been guaranteed to produce reasonable results.In this thesis we consider finite difference methods on summation-by-parts (SBP) form. To impose boundary and interface conditions we use the simultaneous approximation term (SAT) method. The SBP-SAT technique is designed such that the numerical solution mimics the energy estimates satisfied by the true solution. Hence, SBP-SAT schemes are energy-stable by construction and guaranteed to converge to the true solution of well-posed linear PDE. The SBP-SAT framework provides a means to derive high-order methods without jeopardizing stability. Thus, they overcome most of the drawbacks historically associated with finite difference methods.This thesis consists of three parts. The first part is devoted to improving existing SBP-SAT methods. In Papers I and II, we derive schemes with improved accuracy compared to standard schemes. In Paper III, we present an embedded boundary method that makes it easier to cope with complex geometries. The second part of the thesis shows how to apply the SBP-SAT method to wave propagation problems in acoustics (Paper IV) and quantum mechanics (Papers V and VI). The third part of the thesis, consisting of Paper VII, presents an efficient, fully explicit time-integration scheme well suited for locally refined meshes.
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| 18. |
- Almquist, Martin, et al.
(författare)
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Elastic wave propagation in anisotropic solids using energy-stable finite differences with weakly enforced boundary and interface conditions
- 2021
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Ingår i: Journal of Computational Physics. - : Elsevier. - 0021-9991 .- 1090-2716. ; 424
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Tidskriftsartikel (refereegranskat)abstract
- Summation-by-parts (SBP) finite difference methods have several desirable properties for second-order wave equations. They combine the computational efficiency of narrow-stencil finite difference operators with provable stability on curvilinear multiblock grids. While several techniques for boundary and interface conditions exist, weak imposition via simultaneous approximation terms (SATs) is perhaps the most flexible one. Although SBP methods have been applied to elastic wave equations many times, an SBP-SAT method for general anisotropic elastic wave equations has not yet been presented in the literature. We fill this gap by deriving energy-stable self-adjoint SBP-SAT methods for general anisotropic materials on curvilinear multiblock grids. The methods are based on fully compatible SBP operators. Although this paper focuses on classical SBP finite difference operators, the presented boundary and interface treatments are general and apply to a range of methods that satisfy an SBP property. We demonstrate the stability and accuracy properties of a particular set of fully compatible SBP-SAT schemes using the method of manufactured solutions. We also demonstrate the utility of the new method in elastodynamic cloaking and seismic imaging in mountainous regions.
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| 19. |
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| 20. |
- Almquist, Martin
(författare)
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Localization studies for parathyroid surgery
- 2021
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Ingår i: JAMA Otolaryngology - Head and Neck Surgery. - : American Medical Association (AMA). - 2168-6181. ; 147:8, s. 706-707
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Tidskriftsartikel (refereegranskat)
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