| 1. |
- Nordström, Johan, 1992-, et al.
(författare)
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A GPU code for analytic continuation through a sampling method
- 2016
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Ingår i: SoftwareX. - : Elsevier. - 2352-7110. ; 5, s. 178-182
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Tidskriftsartikel (refereegranskat)abstract
- We here present a code for performing analytic continuation of fermionic Green’s functions and self-energies as well as bosonic susceptibilities on a graphics processing unit (GPU). The code is based on the sampling method introduced by Mishchenko et al. (2000), and is written for the widely used CUDA platform from NVidia. Detailed scaling tests are presented, for two different GPUs, in order to highlight the advantages of this code with respect to standard CPU computations. Finally, as an example of possible applications, we provide the analytic continuation of model Gaussian functions, as well as more realistic test cases from many-body physics.
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| 2. |
- Bentzer, Peter, et al.
(författare)
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The volume-expanding effects of autologous liquid stored plasma following hemorrhage.
- 2012
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Ingår i: Scandinavian Journal of Clinical and Laboratory Investigation. - : Informa UK Limited. - 1502-7686 .- 0036-5513. ; 72:6, s. 490-494
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Tidskriftsartikel (refereegranskat)abstract
- Background: Plasma use has increased since studies have suggested that early treatment with blood components in trauma with severe hemorrhage may improve outcome. Plasma is also commonly used to correct coagulation disturbances in non-bleeding patients. Little is known about the effects of plasma transfusion on plasma volume. We report a prospective interventional study in which the plasma volume-expanding effect of autologous plasma was investigated after a controlled hemorrhage. Methods: Plasma obtained by plasmapheresis from nine healthy regular blood donors was stored at 2-6°C. Five weeks after donation the subjects were bled of 600 ml and then transfused with 600 ml of autologous plasma. Plasma volume was estimated using (125)I-albumin before and after bleeding, and immediately after plasma transfusion. Plasma volume changes were then estimated by measuring changes in hematocrit during the following 3-h period. Results: Estimated plasma volume after bleeding was 3170 ± 320 ml and 3690 ± 380 ml (mean ± standard deviation) immediately following the transfusion of plasma (p 0.05). This increase in plasma volume corresponds to 86 ± 13% of the infused volume. Three hours after transfusion, plasma volume was still 3680 ± 410 ml. Conclusions: Stored liquid plasma has a plasma volume expanding effect up to 86% of its infused volume with a duration of at least 3 h.
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| 3. |
- Ekbäck, Gustav, et al.
(författare)
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Tranexamic Acid Reduces Blood Loss in Total Hip Replacement Surgery
- 2000
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Ingår i: Anesthesia and Analgesia. - 0003-2999 .- 1526-7598. ; 91:5, s. 1124-1130
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Tidskriftsartikel (refereegranskat)abstract
- Intraoperatively administered, tranexamic acid (TA) does not reduce bleeding in total hip replacement (THR). Therefore, its prophylactic use was attempted in the present study because this has been shown to be more effective in cardiac surgery. We investigated 40 patients undergoing THR in a prospective, randomized, double-blinded study. Twenty patients received TA given in two bolus doses of 10 mg/kg each, the first just before surgical incision and the second 3 h later. In addition, a continuous infusion of TA, 1.0 mg · kg−1 · h−1 for 10 h, was given after the first bolus dose. The remaining 20 patients formed a control group. Both groups used preoperative autologous blood donation and intraoperative autotransfusion. Intraoperative bleeding was significantly less (P = 0.001) in the TA group compared with the control group (630 ± 220 mL vs 850 ± 260 mL). Postoperative drainage bleeding was correspondingly less (P = 0.001) (520 ± 280 vs 920 ± 410 mL). Up to 10 h postoperatively, plasma D-dimer concentration was halved in the TA group compared with the control group. One patient in each group had an ultrasound-verified late deep vein thrombosis. In conclusion, we found TA, administrated before surgical incision, to be efficient in reducing bleeding during THR.
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| 4. |
- Jana, Somnath, et al.
(författare)
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Charge disproportionate antiferromagnetism at the verge of the insulator-metal transition in doped LaFeO3
- 2019
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 99:7
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Tidskriftsartikel (refereegranskat)abstract
- We explore the effects of electron doping in lanthanum ferrite, LaFeO3 by doping Mo at the Fe sites. Based on magnetic, transport, scanning tunneling spectroscopy, and x-ray photoelectron spectroscopy measurements, we find that the large gap, charge-transfer, antiferromagnetic (AFM) insulator LaFeO3 becomes a small gap AFM band insulator at low Mo doping. With increasing doping concentration, Mo states, which appear around the Fermi level, is broadened and become gapless at a critical doping of 20%. Using a combination of calculations based on density functional theory plus Hubbard U (DFT+U) and x-ray absorption spectroscopy measurements, we find that the system shows charge disproportionation (CD) in Fe ions at 25% Mo doping, where two distinct Fe sites, having Fe2+ and Fe3+ nominal charge states appear. A local breathing-type lattice distortion induces the charge disproportionation at the Fe site without destroying the antiferromagnetic order. Our combined experimental and theoretical investigations establish that the Fe states form a CD antiferromagnet at 25% Mo doping, which remains insulating, while the appearance of Mo states around the Fermi level is showing an indication towards the insulator-metal transition.
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| 5. |
- Jana, Somnath, et al.
(författare)
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Doping induced site-selective Mott insulating phase in LaFeO3
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Tailoring transport properties of strongly correlated electron systems in a controlled fashion counts among the dreams of materials scientists. In copper oxides, vary- ing the carrier concentration is a tool to obtain high- temperature superconducting phases. In manganites, dop- ing results in exotic physics such as insulator-metal tran- sitions (IMT), colossal magnetoresistance (CMR), orbital- or charge-ordered (CO) or charge-disproportionate (CD) states. In most oxides, antiferromagnetic order and CD phase is asssociated with insulating behavior. Here we re- port the realization of a unique physical state that can be induced by Mo doping in LaFeO3: the resulting metallic state is a site-selective Mott insulator where itinerant elec- trons evolving on low-energy Mo states coexist with local- ized carriers on the Fe sites. In addition, a local breathing- type lattice distortion induces charge disproportionation on the latter, without destroying the antiferromagnetic order. A state, combining antiferromangetism, metallic- ity and CD phenomena is rather rare in oxides and have utmost significance for future antiferromagnetic memory devices.
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| 6. |
- Jansohn, Erik, et al.
(författare)
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A pilot study on the applicability of thromboelastometry in detecting brain tumour-induced hypercoagulation
- 2017
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Ingår i: Scandinavian Journal of Clinical and Laboratory Investigation. - : Informa UK Limited. - 0036-5513 .- 1502-7686. ; 77:4, s. 289-294
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Tidskriftsartikel (refereegranskat)abstract
- Patients with intracranial tumours have an increased risk of venous thromboembolism, particularly during the first month after neurosurgery. A proposed explanation for this increased risk, are procoagulant tumour-derived substances, such as tissue factor, usually measured in peripheral blood. The aim of the present study is to investigate whether a rotational thromboelastometry (ROTEM) can measure the procoagulative activity of tumour tissue. The study included 21 patients who were undergoing a craniotomy and complete tumour resection after written consent and ethical approval were obtained. Tumour tissue was biopsied during surgery and used for in vitro spiking of patients own citrated whole blood. Blood samples with or without spiking were analyzed with ROTEM using different activating reagents. ROTEM clotting time significantly decreased (p < .001), indicating a hypercoagulative response on clot initiation that was strongest for glioma tumours. However, ROTEM clot formation time was significantly prolonged (p < .001), which was an opposite response that indicated poor initial clot propagation. ROTEM maximum lysis was increased in the tumour tissue-spiked samples (p < .001), indicating a strong fibrinolytic activity in brain tumour tissue. Tissue extracts from intracranial tumours have both procoagulant and fibrinolytic effects that are detectable with ROTEM. Glioma tumours had the strongest hypercoagulative response in our in vitro model. Larger studies are necessary to test the clinical relevance and accuracy of tumour extract spiked viscoelastic tests to predict the individual patient risk for developing a thrombotic complication.
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| 7. |
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| 8. |
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| 9. |
- Keshavarz, Samara, et al.
(författare)
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Electronic structure, magnetism, and exchange integrals in transition-metal oxides : Role of the spin polarization of the functional in DFT+U calculations
- 2018
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Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 97:18
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory augmented with Hubbard-U corrections (DFT+U) is currently one of the most widely used methods for first-principles electronic structure modeling of insulating transition-metal oxides (TMOs). Since U is relatively large compared to bandwidths, the magnetic excitations in TMOs are expected to be well described by a Heisenberg model. However, in practice the calculated exchange parameters J(ij) depend on the magnetic configuration from which they are extracted and on the functional used to compute them. In this work we investigate how the spin polarization dependence of the underlying exchange-correlation functional influences the calculated magnetic exchange constants of TMOs. We perform a systematic study of the predictions of calculations based on the local density approximation plus U (LDA+U) and the local spin density approximation plus U (LSDA+U) for the electronic structures, total energies, and magnetic exchange interactions Jij extracted from ferromagnetic (FM) and antiferromagnetic (AFM) configurations of several transition-metal oxide materials. We report that for realistic choices of Hubbard U and Hund's J parameters, LSDA+U and LDA+U calculations result in different values of the magnetic exchange constants and band gap. The dependence of the band gap on the magnetic configuration is stronger in LDA+U than in LSDA+U and we argue that this is the main reason why the configuration dependence of Jij is found to be systematically more pronounced in LDA+U than in LSDA+U calculations. We report a very good correspondence between the computed total energies and the parametrized Heisenberg model for LDA+U calculations, but not for LSDA+U, suggesting that LDA+U is a more appropriate method for estimating exchange interactions.
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| 10. |
- Larsson, A., et al.
(författare)
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Comparison of point-of-care hemostatic assays, routine coagulation tests, and outcome scores in critically ill patients
- 2015
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Ingår i: Journal of critical care. - : W B SAUNDERS CO-ELSEVIER INC. - 0883-9441 .- 1557-8615. ; 30:5, s. 1032-1038
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The purposes of the study are to compare point-of-care (POC) hemostatic devices in critically ill patients with routine laboratory tests and intensive care unit (ICU) outcome scoring assessments and to describe the time course of these variables in relation to mortality rate. Materials and methods: Patients admitted to the ICU with a prognosis of more than 3 days of stay were included. The POC devices, Multiplate platelet aggregometry, rotational thromboelastometry, and ReoRox viscoelastic tests, were used. All variables were compared between survivors and nonsurvivors. Point-of-care results were compared to prothrombin time, activated partial thromboplastin time, platelet count, fibrinogen concentration, and Sequential Organ Failure Assessment score and Simplified Acute Physiology Score 3. Results: Blood was sampled on days 0 to 1, 2 to 3, and 4 to 10 from 114 patients with mixed diagnoses during 237 sampling events. Nonsurvivors showed POC and laboratory signs of hypocoagulation and decreased fibrinolysis over time compared to survivors. ReoRox detected differences between survivors and nonsurvivors better than ROTEM and Multiplate. Conclusions: All POC and routine laboratory tests showed a hypocoagulative response in nonsurvivors compared to survivors. ReoRox was better than ROTEM and Multiplate at detecting differences between surviving and nonsurviving ICU patients. However, Simplified Acute Physiology Score 3 showed the best association to mortality outcome.
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| 11. |
- Lüder, Johann, et al.
(författare)
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Theory of L-edge spectroscopy of strongly correlated systems
- 2017
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 96:24
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption spectroscopy measured at the L edge of transition metals (TMs) is a powerful element selective tool providing direct information about the correlation effects in the 3d states. The theoretical modeling of the 2p -> 3d excitation processes remains to be challenging for contemporary ab initio electronic structure techniques, due to strong core-hole and multiplet effects influencing the spectra. In this work, we present a realization of the method combining the density-functional theory with multiplet ligand field theory, proposed in Haverkort et al. [Phys. Rev. B 85, 165113 (2012)]. In this approach, a single-impurity Anderson model (SIAM) is constructed, with almost all parameters obtained from first principles, and then solved to obtain the spectra. In our implementation, we adopt the language of the dynamical mean-field theory and utilize the local density of states and the hybridization function, projected onto TM 3d states, in order to construct the SIAM. The developed computational scheme is applied to calculate the L-edge spectra for several TM monoxides. A very good agreement between the theory and experiment is found for all studied systems. The effect of core-hole relaxation, hybridization discretization, possible extensions of the method as well as its limitations are discussed.
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| 12. |
- Neelakantan, Suraj, 1994-, et al.
(författare)
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Machine Learning for Lithology Analysis using a Multi-Modal Approach of Integrating XRF and XCT data
- 2024
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Ingår i: 14th Scandinavian Conference on Artificial Intelligence SCAI 2024, June 10-11, 2024, Jönköping, Sweden.
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Konferensbidrag (refereegranskat)abstract
- We explore the use of various machine learning (ML) models for classifying lithologies utilizing data from X-ray fluorescence (XRF) and X-ray computed tomography (XCT). Typically, lithologies are identified over several meters, which restricts the use of ML models due to limited training data. To address this issue, we augment the original interval dataset, where lithologies are marked over extensive sections, into finer segments of 10cm, to produce a high resolution dataset with vastly increased sample size. Additionally, we examine the impact of adjacent lithologies on building a more generalized ML model. We also demonstrate that combining XRF and XCT data leads to an improved classification accuracy compared to using only XRF data, which is the common practice in current studies, or solely relying on XCT data.
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| 13. |
- Panda, Swarup K., et al.
(författare)
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A charge self-consistent LDA plus DMFT study of the spectral properties of hexagonal NiS
- 2014
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 16, s. 093049-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure and spectral properties of hexagonal NiS have been studied in the high temperature paramagnetic phase and low temperature anti-ferromagnetic phase. The calculations have been performed using charge self-consistent density-functional theory in local density approximation combined with dynamical mean-field theory (LDA+DMFT). The photoemission spectra (PES) and optical properties have been computed and compared with the experimental data. Our results show that the dynamical correlation effects are important to understand the spectral and optical properties of NiS. These effects have been analyzed in detail by means of the computed real and imaginary part of the self-energy.
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| 14. |
- Schött, Johan, et al.
(författare)
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Analytic continuation by averaging Pade approximants
- 2016
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Ingår i: PHYSICAL REVIEW B. - 2469-9950. ; 93:7
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Tidskriftsartikel (refereegranskat)abstract
- The ill-posed analytic continuation problem for Green's functions and self-energies is investigated by revisiting the Pade approximants technique. We propose to remedy the well-known problems of the Pade approximants by performing an average of several continuations, obtained by varying the number of fitted input points and Pade coefficients independently. The suggested approach is then applied to several test cases, including Sm and Pr atomic self-energies, the Green's functions of the Hubbard model for a Bethe lattice and of the Haldane model for a nanoribbon, as well as two special test functions. The sensitivity to numerical noise and the dependence on the precision of the numerical libraries are analyzed in detail. The present approach is compared to a number of other techniques, i.e., the nonnegative least-squares method, the nonnegative Tikhonov method, and the maximum entropy method, and is shown to perform well for the chosen test cases. This conclusion holds even when the noise on the input data is increased to reach values typical for quantum Monte Carlo simulations. The ability of the algorithm to resolve fine structures is finally illustrated for two relevant test functions.
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| 15. |
- Schött, Johan, 1988-, et al.
(författare)
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Comparison between methods of analytical continuation for bosonic functions
- 2016
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 94
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Tidskriftsartikel (refereegranskat)abstract
- In this article we perform a critical assessment of different known methods for the analytical con- tinuation of bosonic functions, namely the maximum entropy method, the non-negative least-square method, the non-negative Tikhonov method, the Pad ́e approximant method, and a stochastic sam- pling method. Four functions of different shape are investigated, corresponding to four physically relevant scenarios. They include a simple two-pole model function, two flavours of the tight bind- ing model on a square lattice, i.e. a single-orbital metallic system and a two-orbitals insulating system, and the Hubbard dimer. The effect of numerical noise in the input data on the analytical continuation is discussed in detail. Overall, the stochastic method by Mishchenko et al. [Phys. Rev. B 62, 6317 (2000)] is shown to be the most reliable tool for input data whose numerical precision is not known. For high precision input data, this approach is slightly outperformed by the Pad ́e approximant method, which combines a good resolution power with a good numerical stability. Although none of the methods retrieves all features in the spectra in the presence of noise, our analysis provides a useful guideline for obtaining reliable information of the spectral function in cases of practical interest.
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| 16. |
- Schött, Johan
(författare)
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Theoretical and Computational Studies of Strongly Correlated Electron Systems : Dynamical Mean Field Theory, X-ray Absorption Spectroscopy and Analytical Continuation
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis encompasses theoretical and computational studies of strongly correlated elec-tron systems. Understanding how electrons in solids interact with each other is of great im-portance for future technology and other applications. From a fundamental point of view, the Coulomb interaction in a solid leads to a very challenging many-body problem, encapsulating many physical phenomena, e.g. magnetism. Treating this interaction, with a focus on local contributions, is the subject of this thesis. Both models and materials have been investigated, to obtain insight on the mechanisms determining the macroscopic properties of matter. This thesis is divided in four parts, each corresponding to a different project or topic.In the first project a many body method called dynamical mean field theory (DMFT) is used to study the paramagnetic phase of the Hubbard model. A stochastic version of the exact di-agonalization technique is developed for solving the effective impurity model arising in DMFT and generating real frequency spectral functions. In the next project, by combining density functional theory (DFT) with a static solution of the DMFT equations (DFT+U), magnetic ex-change interactions in transition metal oxides (TMOs) are investigated. The spin dependence of the functional is shown to be important for mapping magnetic excitations form the quantum mechanical system to a classical model.The next topic in this thesis concerns the x-ray absorption spectroscopy of TMOs. Spectral functions, in good agreement with experimental data, are calculated by combining DFT with multiplet ligand field theory (MLFT). The effects of the presence of a core-hole are studied in detail for NiO, as well as double counting issues related to higher order terms of the multiple ex-pansion of the Coulomb interaction. A strained induced linearly polarized spectrum is obtained for CaTiO3. Lastly, charge disproportionation is seen in Mo doped LaFeO3.Finally, a critical step in DMFT, called analytical continuation, to obtain physical observ-ables of interest is investigated. Analytical continuation means a transformation of a function in the complex plane. Several methods for performing this transformation are explained, and in particular steps for improving the robustness and accuracy of the Padé approximant method are described.
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