92 research outputs found
Eclipsing Binaries in Open Clusters
Detached eclipsing binaries are very useful objects for calibrating
theoretical stellar models and checking their predictions. Detached eclipsing
binaries in open clusters are particularly important because of the additional
constraints on their age and chemical composition from their membership of the
cluster. I compile a list containing absolute parameters of well-studied
eclipsing binaries in open clusters, and present new observational data on the
B-type systems V1481 Cyg and V2263 Cyg which are members of the young open
cluster NGC 7128.Comment: 4 pages, 2 colour figures. Poster presentation for IAUS 240 (Binary
Stars as Critical Tools and Tests in Contemporary Astrophysics), Prague,
August 2006. The poster itself can be dowloaded in ppt and pdf versions from
http://www.astro.keele.ac.uk/~jkt/pubs.htm
Fast computation of Bernoulli, Tangent and Secant numbers
We consider the computation of Bernoulli, Tangent (zag), and Secant (zig or
Euler) numbers. In particular, we give asymptotically fast algorithms for
computing the first n such numbers in O(n^2.(log n)^(2+o(1))) bit-operations.
We also give very short in-place algorithms for computing the first n Tangent
or Secant numbers in O(n^2) integer operations. These algorithms are extremely
simple, and fast for moderate values of n. They are faster and use less space
than the algorithms of Atkinson (for Tangent and Secant numbers) and Akiyama
and Tanigawa (for Bernoulli numbers).Comment: 16 pages. To appear in Computational and Analytical Mathematics
(associated with the May 2011 workshop in honour of Jonathan Borwein's 60th
birthday). For further information, see
http://maths.anu.edu.au/~brent/pub/pub242.htm
The Biology Instrument for the Viking Mars Mission
Two Viking spacecraft have successfully soft landed on the surface of Mars. Each carries, along with other scientific instruments, one biology laboratory with three different experiments designed to search for evidence of living microorganisms in material sampled from the Martian surface. This 15.5-kg biology instrument which occupies a volume of almost 28.3 dm3 is the first to carry out an in situ search for extraterrestrial life on a planet. The three experiments are called the pyrolytic release, labeled release, and gas exchange. The pyrolytic release experiment has the capability to measure the fixation of carbon dioxide or carbon monoxide into organic matter. The labeled release experiment detects metabolic processes by monitoring the production of volatile carbon compounds from a radioactively labeled nutrient mixture. The gas exchange experiment monitors the gas changes in the head space above a soil sample which is either incubated in a humid environment or supplied with a rich organic nutrient solution. Each experiment can analyze a soil sample as it is received from the surface or, as a control, analyze a soil which has been heated to above 160C. Each instrument has the capability to receive four different soils dug from the Martian surface and perform a number of analysis cycles depending on the particular experiment. This paper describes in detail the design and operation of the three experiments and the supporting subsystems
Advances in ab-initio theory of Multiferroics. Materials and mechanisms: modelling and understanding
Within the broad class of multiferroics (compounds showing a coexistence of
magnetism and ferroelectricity), we focus on the subclass of "improper
electronic ferroelectrics", i.e. correlated materials where electronic degrees
of freedom (such as spin, charge or orbital) drive ferroelectricity. In
particular, in spin-induced ferroelectrics, there is not only a {\em
coexistence} of the two intriguing magnetic and dipolar orders; rather, there
is such an intimate link that one drives the other, suggesting a giant
magnetoelectric coupling. Via first-principles approaches based on density
functional theory, we review the microscopic mechanisms at the basis of
multiferroicity in several compounds, ranging from transition metal oxides to
organic multiferroics (MFs) to organic-inorganic hybrids (i.e. metal-organic
frameworks, MOFs)Comment: 22 pages, 9 figure
School dropout, problem behaviour and poor academic achievement : a longitudinal view of portuguese male offenders
This study examines school drop outs from the perspective of male adults
themselves through interviews with offenders currently serving sentences. Participants
were 10 Portuguese male inmates, between the ages of 19 and 46 years of age,
incarcerated in two prison facilities of the Azores. Qualitative and interpretative methods
were carried out using a semi-structured in-depth individual interview that was audiorecorded
and conducted on the basis of a list of topics. Interview transcripts and thematic
analysis were used in data treatment and analysis. The findings primarily indicate that
poor academic achievement and emotional and behavioural difficulties of participants
played a particular role in early school drop out. The trajectories these individuals
followed within the education system presented problem behaviour, learning disabilities,
and/or foster care interventions. While school drop out circumstances were apparently
various, analysis showed that they were underpinned by three distinct sets of conditions
generally not addressed by the education system. The analysis of the triggering factors
and the maintenance dynamics of school drop outs indicated three distinct types:
retention/absenteeism, life turning points and positive resolution. Implications for
secondary prevention and screening practices are discussed.FCT (SFRH/ BD/ 44245/ 2008)CIEC - unidade de investigação 317 da FC
The Scientific Foundations of Forecasting Magnetospheric Space Weather
The magnetosphere is the lens through which solar space weather phenomena are focused and directed towards the Earth. In particular, the non-linear interaction of the solar wind with the Earth's magnetic field leads to the formation of highly inhomogenous electrical currents in the ionosphere which can ultimately result in damage to and problems with the operation of power distribution networks. Since electric power is the fundamental cornerstone of modern life, the interruption of power is the primary pathway by which space weather has impact on human activity and technology. Consequently, in the context of space weather, it is the ability to predict geomagnetic activity that is of key importance. This is usually stated in terms of geomagnetic storms, but we argue that in fact it is the substorm phenomenon which contains the crucial physics, and therefore prediction of substorm occurrence, severity and duration, either within the context of a longer-lasting geomagnetic storm, but potentially also as an isolated event, is of critical importance. Here we review the physics of the magnetosphere in the frame of space weather forecasting, focusing on recent results, current understanding, and an assessment of probable future developments.Peer reviewe
Overview of Solar Wind–Magnetosphere–Ionosphere–Atmosphere Coupling and the Generation of Magnetospheric Currents
A Study of the Young Quadruple System AO Vel with a ZAMS Eclipsing BpSi Primary and PMS Companions
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