University of St Andrews

About: University of St Andrews is a education organization based out in St Andrews, Fife, United Kingdom. It is known for research contribution in the topics: Population & Laser. The organization has 16260 authors who have published 43364 publications receiving 1636072 citations. The organization is also known as: St Andrews University & University of St. Andrews.

CSI 2264: SIMULTANEOUS OPTICAL AND INFRARED LIGHT CURVES OF YOUNG DISK-BEARING STARS IN NGC 2264 WITH CoRoT and SPITZER—EVIDENCE FOR MULTIPLE ORIGINS OF VARIABILITY*

Abstract: We present the Coordinated Synoptic Investigation of NGC 2264, a continuous 30 day multi-wavelength photometric monitoring campaign on more than 1000 young cluster members using 16 telescopes. The unprecedented combination of multi-wavelength, high-precision, high-cadence, and long-duration data opens a new window into the time domain behavior of young stellar objects. Here we provide an overview of the observations, focusing on results from Spitzer and CoRoT. The highlight of this work is detailed analysis of 162 classical T Tauri stars for which we can probe optical and mid-infrared flux variations to 1% amplitudes and sub-hour timescales. We present a morphological variability census and then use metrics of periodicity, stochasticity, and symmetry to statistically separate the light curves into seven distinct classes, which we suggest represent different physical processes and geometric effects. We provide distributions of the characteristic timescales and amplitudes and assess the fractional representation within each class. The largest category (>20%) are optical "dippers" with discrete fading events lasting ~1-5 days. The degree of correlation between the optical and infrared light curves is positive but weak; notably, the independently assigned optical and infrared morphology classes tend to be different for the same object. Assessment of flux variation behavior with respect to (circum)stellar properties reveals correlations of variability parameters with Hα emission and with effective temperature. Overall, our results point to multiple origins of young star variability, including circumstellar obscuration events, hot spots on the star and/or disk, accretion bursts, and rapid structural changes in the inner disk.

Frequency of solar-like systems and of ice and gas giants beyond the snow line from high-magnification microlensing events in 2005-2008

Abstract: We present the first measurement of the planet frequency beyond the "snow line," for the planet-to-star mass-ratio interval –4.5 200) microlensing events during 2005-2008. The sampled host stars have a typical mass M_(host) ~ 0.5 M_⊙, and detection is sensitive to planets over a range of planet-star-projected separations (s ^(–1)_(max)R_E, s_(max)R_E), where R_E ~ 3.5 AU(M_(host)/M_⊙)^(1/2) is the Einstein radius and s_(max) ~ (q/10^(–4.3))^(1/3). This corresponds to deprojected separations roughly three times the "snow line." We show that the observations of these events have the properties of a "controlled experiment," which is what permits measurement of absolute planet frequency. High-magnification events are rare, but the survey-plus-follow-up high-magnification channel is very efficient: half of all high-mag events were successfully monitored and half of these yielded planet detections. The extremely high sensitivity of high-mag events leads to a policy of monitoring them as intensively as possible, independent of whether they show evidence of planets. This is what allows us to construct an unbiased sample. The planet frequency derived from microlensing is a factor 8 larger than the one derived from Doppler studies at factor ~25 smaller star-planet separations (i.e., periods 2-2000 days). However, this difference is basically consistent with the gradient derived from Doppler studies (when extrapolated well beyond the separations from which it is measured). This suggests a universal separation distribution across 2 dex in planet-star separation, 2 dex in mass ratio, and 0.3 dex in host mass. Finally, if all planetary systems were "analogs" of the solar system, our sample would have yielded 18.2 planets (11.4 "Jupiters," 6.4 "Saturns," 0.3 "Uranuses," 0.2 "Neptunes") including 6.1 systems with two or more planet detections. This compares to six planets including one two-planet system in the actual sample, implying a first estimate of 1/6 for the frequency of solar-like systems.

Magnetohydrodynamics of the Sun

Abstract: Magnetohydrodynamics of the Sun is a completely new up-to-date rewrite from scratch of the 1982 book Solar Magnetohydrodynamics, taking account of enormous advances in understanding since that date It describes the subtle and complex interaction between the Sun's plasma atmosphere and its magnetic field, which is responsible for many fascinating dynamic phenomena Chapters cover the generation of the Sun's magnetic field by dynamo action, magnetoconvection and the nature of photospheric flux tubes such as sunspots, the heating of the outer atmosphere by waves or reconnection, the structure of prominences, the nature of eruptive instability and magnetic reconnection in solar flares and coronal mass ejections, and the acceleration of the solar wind by reconnection or wave-turbulence It is essential reading for graduate students and researchers in solar physics and related fields of astronomy, plasma physics and fluid dynamics Problem sets and other resources are available at wwwcambridgeorg/9780521854719

Structure of the polymer electrolyte poly(ethylene oxide)6:LiAsF6

Abstract: Polymer electrolytes—salts (such as LiCF3SO3) dissolved in solid, high-molar-mass polymers (for example, poly(ethylene oxide), PEO)1,2,3—hold the key to the development of all-solid-state rechargeable lithium batteries4. They also represent an unusual class of coordination compounds in the solid state5. Conductivities of up to 10−4 S cm−1 may be obtained, but higher levels are needed for applications in batteries5,6,7. To achieve such levels requires a better understanding of the conduction mechanism, and crucial to this is a knowledge of polymer-electrolyte structure. Crystalline forms of polymer electrolytes are obtained at only a few discrete compositions. The structures of 3 : 1 and 4 : 1 complexes (denoting the ratio of ether oxygens to cations) have been determined5,8,9. But the 6 : 1 complex is of greater interest as the conductivity of polymer electrolytes increases significantly on raising the polymer content from 3 : 1 to 6 : 1 (refs 10, 11). Furthermore, many highly conducting polymer-electrolyte systems form crystalline 6 : 1 complexes whereas those with lower conductivities do not. Here we report the structure of the PEO:LiAsF6 complex with a 6 : 1 composition. Determination of the structure was carried out abinitio by employing a method for flexible molecular structures, involving full profile fitting to the X-ray powder diffraction data by simulated annealing12. Whereas in the 3 : 1 complexes the polymer chains form helices, those in the 6 : 1 complex form double non-helical chains which interlock to form a cylinder. The lithium ions reside inside these cylinders and, in contrast to other complexes, are not coordinated by the anions.

The Consequence of Tree Pests and Diseases for Ecosystem Services

Abstract: Background Trees are major components of many terrestrial ecosystems and are grown in managed plantations and orchards to provide a variety of economically important products, including timber, pulp, fiber, and food. They are subject to a wide range of pests and diseases, of which the most important causative agents are viruses, bacteria, fungi, oomycetes, and insect herbivores. Research on tree pests and diseases has had a historical focus on trees of direct economic importance. However, some epidemics and infestations have damaged and killed common trees that are integral parts of natural ecosystems. These have harmed valuable landscapes and highlighted the wide-ranging consequences arising from tree pests and diseases. There is also growing concern that aspects of globalization—in particular, higher volumes and new forms of trade—may increase the risk of disease spread. A forest providing numerous ecosystem services is subject to a disease epidemic that reduces the abundance of a dominant native species, resulting in a change in forest structure. Initially, a wide range of ecosystem services (A to D) are harmed. But as trees grow to replace lost species, some (perhaps carbon storage or water purification) are regained, whereas others (perhaps the biodiversity supported by the diseased tree species) are permanently disrupted. Policy measures can both help prevent new diseases being introduced (the first stage) or improve recovery through management practices or planting resistant trees. Advances We review the challenges in maintaining tree health in natural and managed ecosystems. It is argued that it is helpful to consider explicitly the consequences of pests and diseases for the full range of ecosystem services provided by trees. In addition to forest and orchard products, tree pests and diseases can affect the ability of forests to sequester and store carbon, reduce flood risk, and purify water. They can affect the biodiversity supported by trees and the recreational and cultural values accorded to woodland by people. Many of these benefits are uncosted and enjoyed by different classes of stakeholders, which raises difficult questions about who should be responsible for measures to protect tree health. Changes in the risk of pest and disease introduction, the increasing prevalence of genetic reassortment leading to novel disease threats, and the potential role of climate change are all highlighted. Outlook Modern pest and disease management is based on an extensive science base that is rapidly developing, spurred in particular by modern molecular technologies. A research priority is to build a better understanding of why certain pathogens and insects become major pests and diseases. This will involve a better understanding of the molecular basis of pathogenicity and herbivory, as will ecological insights into why some species reach epidemic prevalence or abundance. It will also help anticipate which species may become a problem if they are transported to new geographical regions, recombine with other organisms, or experience new climatic conditions. However, identifying all species that may become pests will be impossible, and the Review stresses the importance of risk management at the “pathway of introduction” level, especially when modern trade practices provide potential new routes of entry. Last, when ecosystem services are provided by woods and forests rather than individual tree species, we need to understand better the consequences of pests and diseases that attack or feed on particular species.