Finding Close Encounters: Toward a Consensus on the Influence of Stellar Flybys on the Solar System over 10 Million Years

This thesis is a study of possible stellar encounters of the Sun, both in the past and in the future within ± 10 Myr of the current epoch. This study is based on data gleaned from the first Gaia data release (Gaia DR1). One of the components of the Gaia DR1 is the TGAS catalogue. TGAS contained five astrometric parameters for more than two million stars. Four separate catalogues were used to provide radial velocities for these stars. A linear motion approximation was used to make a cut within an initial catalogue keeping only the stars that would have perihelia within 10 pc. 1003 stars were found to have a perihelion distance less than 10 pc. Each of these stars was then cloned 1000 times from their covariance matrix from Gaia DR1. The stars’ orbits were numerically integrated through a model galactic potential. After the integration, a particularly interesting set of candidates was selected for deeper study. In particular stars with a mean perihelion distance less than 2 pc were chosen for a deeper study since they will have significant influence on the Oort cloud. 46 stars were found to have a mean perihelion distance less than 2 pc. Among them HIP 89825 (GL 710) still remains the closest encounter with a Solar System with a perihelion of 0.4-0.8 pc, 1.35 Myr in the future. A principal component analysis was performed in order to show the distribution of the clones around the Oort cloud. The thesis also looks into the influence of the solar apex motion on the distribution of encounter perihelia directions. Some new close encounters have been identified and refinements have been made on encounters reported in previous studies

The long reign of the United States is over; the 21st century belongs to China

United States has been the global leader since overtaking Britain in 1871. Recently economists are anticipating China could be the global leader by 2019 as US is on the edge of losing its status of largest economy in the world.  This paper focuses on the current situation of these two emperors to identify whether China could overtake US economy—an outstanding controversial issue. Keywords: global economic power, US economy, China econom

HiFLEx – a highly flexible package to reduce cross-dispersed Echelle spectra

© 2020 The Astronomical Society of the Pacific. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence (https://creativecommons.org/licenses/by/3.0/). Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.We describe a flexible data reduction package for high resolution cross-dispersed echelle data. This open-source package is developed in Python and includes optional GUIs for most of the steps. It does not require any pre-knowledge about the form or position of the echelle-orders. It has been tested on cross-dispersed echelle spectrographs between 13k and 115k resolution (bifurcated fiber-fed spectrogaph ESO-HARPS and single fiber-fed spectrograph TNT-MRES). HiFLEx can be used to determine radial velocities and is designed to use the TERRA package but can also control the radial velocity packages such as CERES and SERVAL to perform the radial velocity analysis. Tests on HARPS data indicates radial velocities results within ±3ms−1 of the literature pipelines without any fine tuning of extraction parameters.Peer reviewe

Efficacy of self-monitored blood pressure, with or without telemonitoring, for titration of antihypertensive medication (TASMINH4): an unmasked randomised controlled trial.

BACKGROUND: Studies evaluating titration of antihypertensive medication using self-monitoring give contradictory findings and the precise place of telemonitoring over self-monitoring alone is unclear. The TASMINH4 trial aimed to assess the efficacy of self-monitored blood pressure, with or without telemonitoring, for antihypertensive titration in primary care, compared with usual care. METHODS: This study was a parallel randomised controlled trial done in 142 general practices in the UK, and included hypertensive patients older than 35 years, with blood pressure higher than 140/90 mm Hg, who were willing to self-monitor their blood pressure. Patients were randomly assigned (1:1:1) to self-monitoring blood pressure (self-montoring group), to self-monitoring blood pressure with telemonitoring (telemonitoring group), or to usual care (clinic blood pressure; usual care group). Randomisation was by a secure web-based system. Neither participants nor investigators were masked to group assignment. The primary outcome was clinic measured systolic blood pressure at 12 months from randomisation. Primary analysis was of available cases. The trial is registered with ISRCTN, number ISRCTN 83571366. FINDINGS: 1182 participants were randomly assigned to the self-monitoring group (n=395), the telemonitoring group (n=393), or the usual care group (n=394), of whom 1003 (85%) were included in the primary analysis. After 12 months, systolic blood pressure was lower in both intervention groups compared with usual care (self-monitoring, 137·0 [SD 16·7] mm Hg and telemonitoring, 136·0 [16·1] mm Hg vs usual care, 140·4 [16·5]; adjusted mean differences vs usual care: self-monitoring alone, -3·5 mm Hg [95% CI -5·8 to -1·2]; telemonitoring, -4·7 mm Hg [-7·0 to -2·4]). No difference between the self-monitoring and telemonitoring groups was recorded (adjusted mean difference -1·2 mm Hg [95% CI -3·5 to 1·2]). Results were similar in sensitivity analyses including multiple imputation. Adverse events were similar between all three groups. INTERPRETATION: Self-monitoring, with or without telemonitoring, when used by general practitioners to titrate antihypertensive medication in individuals with poorly controlled blood pressure, leads to significantly lower blood pressure than titration guided by clinic readings. With most general practitioners and many patients using self-monitoring, it could become the cornerstone of hypertension management in primary care. FUNDING: National Institute for Health Research via Programme Grant for Applied Health Research (RP-PG-1209-10051), Professorship to RJM (NIHR-RP-R2-12-015), Oxford Collaboration for Leadership in Applied Health Research and Care, and Omron Healthcare UK

Environmental variation of the low-mass IMF

We use a series of magnetohydrodynamic simulations including both radiative and protostellar outflow feedback to study the environmental variation of the initial mass function. The simulations represent a carefully-controlled experiment whereby we keep all dimensionless parameters of the flow constant except for those related to feedback. We show that radiation feedback suppresses the formation of lower mass objects more effectively as the surface density increases, but this only partially compensates for the decreasing Jeans mass in denser environments. Similarly, we find that protostellar outflows are more effective at suppressing the formation of massive stars in higher surface density environments. The combined effect of these two trends is towards an IMF with a lower characteristic mass and a narrower overall mass range in high surface density environments. We discuss the implications of these findings for the interpretation of observational evidence of IMF variation in early-type galaxies