Teemu Laakso

Bio: Teemu Laakso is an academic researcher from University of Helsinki. The author has contributed to research in topics: Aortic valve replacement & Valve replacement. The author has an hindex of 8, co-authored 24 publications receiving 229 citations.

Asteroid orbits using phase-space volumes of variation

Abstract: We present a statistical orbit computation technique for asteroids with transitional observational data, that is, a moderate number of data points spanning a moderate observational time interval. With the help of local least-squares solutions in the phase space of the orbital elements, we map the volume of variation as a function of one or more of the elements. We sample the resulting volume using a Monte Carlo technique and, with proper weights for the sample orbital elements, characterize the six-dimensional orbital-element probability density function. The volume-of-variation (VOV) technique complements the statistical ranging technique for asteroids with exiguous observational data (short time intervals and/or small numbers of observations) and the least-squares technique for extensive observational data. We show that, asymptotically, results using the new technique agree closely with those from ranging and least squares. We apply the technique to the near-Earth object 2004 HA 39 , the main-belt object 2004 QR and the transneptunian object 2002 CX 224 recently observed at the Nordic Optical Telescope on La Palma, illustrating the potential of the technique in ephemeris prediction. The VOV technique helps us assess the phase transition in orbital-element probability densities, that is, the non-linear collapse of wide orbital-element distributions to narrow localized ones. For the three objects above, the transition takes place for observational time intervals of the order of 10 h, 5 d and 10 months, respectively, emphasizing the significance of the orbital-arc fraction covered by the observations.

Prosthetic valve endocarditis after transcatheter or surgical aortic valve replacement with a bioprosthesis: results from the FinnValve Registry

Abstract: Aims The aim of this study was to compare the risk of prosthetic valve endocarditis (PVE) in patients with transcatheter aortic valve replacement (TAVR) or surgical aortic valve replacement (SAVR). Methods and results The FinnValve registry included data from 6,463 consecutive patients who underwent TAVR (n=2,130) or SAVR (n=4,333) with a bioprosthesis from 2008 to 2017. PVE was defined according to the modified Duke criteria. In this study, the incidence of PVE was 3.4/1,000 person-years after TAVR, and 2.9/1,000 person-years after SAVR. In competing risk analysis there was no significant difference in the risk of PVE between patients with TAVR and SAVR over an eight-year observational period. Male gender (HR 1.73, 95% CI: 1.04-2.89) and deep sternal wound infection or vascular access-site infection (HR 5.45, 95% CI: 2.24-13.2) were positively associated with PVE, but not type of procedure (HR 1.09, 95% CI: 0.59-2.01) in multivariate analysis. The mortality rate was 37.7% at one month and increased to 52.5% at one year. Surgical treatment was independently associated with decreased in-hospital mortality (HR 0.34, 95% CI: 0.21-0.61). Conclusions PVE is rare, and its risk is similar after TAVR and SAVR. ClinicalTrials.gov Identifier: NCT03385915. https://clinicaltrials.gov/ct2/show/NCT03385915.

Gravitational scattering by giant planets

Abstract: We seek to characterize giant-planet systems by their gravitational scattering properties. We do this to a given system by integrating it numerically along with a large number of hypothetical small bodies that are initially in eccentric habitable zone (HZ)-crossing orbits. Our analysis produces a single number, the escape rate, which represents the rate at which the small-body flux is perturbed away by the giant planets into orbits that no longer pose a threat to terrestrial planets inside the HZ. Obtaining the escape rate this way is similar to computing the largest Liapunov exponent as the exponential rate of divergence of two nearby orbits. For a terrestrial planet inside the HZ, the escape rate value quantifies the “protective” effect that the studied giant-planet system offers. Therefore, escape rates could provide information on whether certain giant-planet configurations produce a more desirable environment for life than the others. We present some computed escape rates on selected planetary systems, focusing on effects of varying the masses and semi-major axes of the giant planets. In the case of our Solar System we find rather surprisingly that Jupiter, in its current orbit, may provide a minimal amount of protection to the Earth.

Comparison of Outcomes After Transcatheter Aortic Valve Replacement vs Surgical Aortic Valve Replacement Among Patients With Aortic Stenosis at Low Operative Risk

Abstract: Importance Transcatheter aortic valve replacement (TAVR) has been shown to be a valid alternative to surgical aortic valve replacement (SAVR) in patients at high operative risk with severe aortic stenosis (AS). However, the evidence of the benefits and harms of TAVR in patients at low operative risk is still scarce. Objective To compare the short-term and midterm outcomes after TAVR and SAVR in low-risk patients with AS. Design, Setting, and Participants This retrospective comparative effectiveness cohort study used data from the Nationwide Finnish Registry of Transcatheter and Surgical Aortic Valve Replacement for Aortic Valve Stenosis of patients at low operative risk who underwent TAVR or SAVR with a bioprosthesis for severe AS from January 1, 2008, to November 30, 2017. Low operative risk was defined as a Society of Thoracic Surgeons Predicted Risk of Mortality score less than 3% without other comorbidities of clinical relevance. One-to-one propensity score matching was performed to adjust for baseline covariates between the TAVR and SAVR cohorts. Exposures Primary TAVR or SAVR with a bioprosthesis for AS with or without associated coronary revascularization. Main Outcomes and Measures The primary outcomes were 30-day and 3-year survival. Results Overall, 2841 patients (mean [SD] age, 74.0 [6.2] years; 1560 [54.9%] men) fulfilled the inclusion criteria and were included in the analysis; TAVR was performed in 325 patients and SAVR in 2516 patients. Propensity score matching produced 304 pairs with similar baseline characteristics. Third-generation devices were used in 263 patients (86.5%) who underwent TAVR. Among these matched pairs, 30-day mortality was 1.3% after TAVR and 3.6% after SAVR (P = .12). Three-year survival was similar in the study cohorts (TAVR, 85.7%; SAVR, 87.7%;P = .45). Interaction tests found no differences in terms of 3-year survival between the study cohorts in patients younger than vs older than 80 years or in patients who received recent aortic valve prostheses vs those who did not. Conclusions and Relevance Transcatheter aortic valve replacement using mostly third-generation devices achieved similar short- and mid-term survival compared with SAVR in low-risk patients. Further studies are needed to assess the long-term durability of TAVR prostheses before extending their use to low-risk patients.

M stars as targets for terrestrial exoplanet searches and biosignature detection.

Abstract: The changing view of planets orbiting low mass stars, M stars, as potentially hospitable worlds for life and its remote detection was motivated by several factors, including the demonstration of viable atmospheres and oceans on tidally locked planets, normal incidence of dust disks, including debris disks, detection of planets with masses in the 5–20 M⊕ range, and predictions of unusually strong spectral biosignatures We present a critical discussion of M star properties that are relevant for the longand short-term thermal, dynamical, geological, and environmental stability of conventional liquid water habitable zone (HZ) M star planets, and the advantages and disadvantages of M stars as targets in searches for terrestrial HZ planets using various detection techniques Biological viability seems supported by unmatched very long-term stability conferred by tidal locking, small HZ size, an apparent short-fall of gas giant planet perturbers, immunity to large astrosphere compressions, and several other fact

An Introduction to Chaos in Nonequilibrium Statistical Mechanics

Abstract: Preface 1. Non-equilibrium statistical mechanics 2. The Boltzmann equation 3. Liouville's equation 4. Poincare recurrence theorem 5. Boltzmann's ergodic hypothesis 6. Gibbs' picture-mixing systems 7. The Green-Kubo formulae 8. The Baker's transformation 9. Lyapunov exponents for a map 10. The Baker's transformation is ergodic 11. Kolmogorov-Sinai entropy 12. The Frobenius-Perron equation 13. Open systems and escape-rates 14. Transport coefficients and chaos 15. SRB and Gibbs measures 16. Fractal forms in Green-Kubo relations 17. Unstable periodic orbits 18. Lorentz lattice gases 19. Dynamical foundations of the Boltzmann equation 20. The Boltzmann equation returns 21. What's next Appendices Bibliography.

Habitability: a review

Abstract: Habitability is a widely used word in the geoscience, planetary science, and astrobiology literature, but what does it mean? In this review on habitability, we define it as the ability of an environment to support the activity of at least one known organism. We adopt a binary definition of “habitability” and a “habitable environment.” An environment either can or cannot sustain a given organism. However, environments such as entire planets might be capable of supporting more or less species diversity or biomass compared with that of Earth. A clarity in understanding habitability can be obtained by defining instantaneous habitability as the conditions at any given time in a given environment required to sustain the activity of at least one known organism, and continuous planetary habitability as the capacity of a planetary body to sustain habitable conditions on some areas of its surface or within its interior over geological timescales. We also distinguish between surface liquid water worlds (suc...