Magnetic Structure of Rapidly Rotating FK Comae-Type Coronae

We present a three-dimensional simulation of the corona of an FK Com-type rapidly rotating G giant using a magnetohydrodynamic model that was originally developed for the solar corona in order to capture the more realistic, non-potential coronal structure. We drive the simulation with surface maps for the radial magnetic field obtained from a stellar dynamo model of the FK Com system. This enables us to obtain the coronal structure for different field topologies representing different periods of time. We find that the corona of such an FK Com-like star, including the large scale coronal loops, is dominated by a strong toroidal component of the magnetic field. This is a result of part of the field being dragged by the radial outflow, while the other part remains attached to the rapidly rotating stellar surface. This tangling of the magnetic field,in addition to a reduction in the radial flow component, leads to a flattening of the gas density profile with distance in the inner part of the corona. The three-dimensional simulation provides a global view of the coronal structure. Some aspects of the results, such as the toroidal wrapping of the magnetic field, should also be applicable to coronae on fast rotators in general, which our study shows can be considerably different from the well-studied and well-observed solar corona. Studying the global structure of such coronae should also lead to a better understanding of their related stellar processes, such as flares and coronal mass ejections, and in particular, should lead to an improved understanding of mass and angular momentum loss from such systems.Comment: Accepted to ApJ, 10 pages, 6 figure

Measuring differential rotation of the K-giant ζ\zeta\,And

We investigate the temporal spot evolution of the K-giant component in the RS CVn-type binary system $\zeta$\,Andromedae to establish its surface differential rotation. Doppler imaging is used to study three slightly overlapping spectroscopic datasets, obtained independently at three different observing sites. Each dataset covers one full stellar rotation with good phase coverage, and in total, results in a continuous coverage of almost three stellar rotations ($P_{\rm rot}=$17.8\,d). Therefore, these data are well suited for reconstructing surface temperature maps and studying temporal evolution in spot configurations. Surface differential rotation is measured by the means of cross-correlation of all the possible image pairs. The individual Doppler reconstructions well agree in the revealed spot pattern, recovering numerous low latitude spots with temperature contrasts of up to $\approx$1000\,K with respect to the unspotted photosphere, and also an asymmetric polar cap which is diminishing with time. Our detailed cross-correlation study consistently indicate solar-type differential rotation with an average surface shear $\alpha\approx0.055$, in agreement with former results.Comment: accepted for publication in A&A, 4 pages, 3 figure

A search for flares and mass ejections on young late-type stars in the open cluster Blanco-1

We present a search for stellar activity (flares and mass ejections) in a sample of 28 stars in the young open cluster Blanco-1. We use optical spectra obtained with ESO's VIMOS multi-object spectrograph installed on the VLT. From the total observing time of $\sim$ 5 hours, we find four H$\alpha$ flares but no distinct indication of coronal mass ejections (CMEs) on the investigated dK-dM stars. Two flares show "dips" in their light-curves right before their impulsive phases which are similar to previous discoveries in photometric light-curves of active dMe stars. We estimate an upper limit of $<$4 CMEs per day per star and discuss this result with respect to a semi- empirical estimation of the CME rate of main-sequence stars. We find that we should have detected at least one CME per star with a mass of 1-15$\times10^{16}$ g depending on the star's X-ray luminosity, but the estimated H$\alpha$ fluxes associated with these masses are below the detection limit of our observations. We conclude that the parameter which mainly influences the detection of stellar CMEs using the method of Doppler-shifted emission caused by moving plasma is not the spectral resolution or velocity but the flux or mass of the CME.Comment: Accepted for publication in MNRAS, accepted 2014 June 10, received 2014 June 5, in original form 2014 March 24, 14 pages, 5 figure

Investigating magnetic activity in very stable stellar magnetic fields: long-term photometric and spectroscopic study of the fully convective M4 dwarf V374 Peg

The ultrafast-rotating ($P_\mathrm{rot}\approx0.44 d$) fully convective single M4 dwarf V374 Peg is a well-known laboratory for studying intense stellar activity in a stable magnetic topology. As an observable proxy for the stellar magnetic field, we study the stability of the light curve, and thus the spot configuration. We also measure the occurrence rate of flares and coronal mass ejections (CMEs). We analyse spectroscopic observations, $BV(RI)_C$ photometry covering 5 years, and additional $R_C$ photometry that expands the temporal base over 16 years. The light curve suggests an almost rigid-body rotation, and a spot configuration that is stable over about 16 years, confirming the previous indications of a very stable magnetic field. We observed small changes on a nightly timescale, and frequent flaring, including a possible sympathetic flare. The strongest flares seem to be more concentrated around the phase where the light curve indicates a smaller active region. Spectral data suggest a complex CME with falling-back and re-ejected material, with a maximal projected velocity of $\approx$675km/s. We observed a CME rate much lower than expected from extrapolations of the solar flare-CME relation to active stars.Comment: 15 figures, 4 tables, accepted for publication in A&

Murtodifferentiaaliyhtälöiden numeerinen ratkaiseminen

Tiivistelmä. Murtodifferentiaaliyhtälö on differentiaaliyhtälö, jossa esiintyy derivaattoja, joiden kertaluku ei ole kokonaisluku. Tämän kaltaisilla yhtälöillä voidaan mallintaa ilmiöitä, joissa esiintyy muistia. Tällöin ilmiön tuleva käyttäytyminen riippuu sen hetkisen tilanteen lisäksi myös aikaisemmasta käyttäytymisestä. Ilmiöitä, joissa esiintyy muistia, on mahdollista löytää esimerkiksi sähkömagnetismin, kvanttifysiikan ja lääketieteen aloilta. Tässä työssä tutustutaan murtodifferentiaaliyhtälöiden perusteisiin niin teorian kuin käytännönkin osalta. Teorian osalta esitellään tunnetuimmat määritelmät ja työkalut, jotka ovat myös välttämättömiä numeeristen laskenta-algoritmien ymmärtämisessä. Murtodifferentiaaliyhtälöitä käsiteltäessä murtoderivaatan ja -integraalin määritelmät ovat keskeisiä. Näitä määritelmiä on useita erilaisia ja tässä tutkielmassa lähdetään liikkeelle Riemann-Liouvillen esitystavoista. Käytännön sovellusten kannalta, ja sen vuoksi myös tämän työn keskeisin käsitelty määritelmä, on kuitenkin Caputon derivaatta, joka mahdollistaa luonnollisen tavan käsitellä alkuarvotehtäviä. Käytännön osuus tässä työssä alustetaan tutustumalla muutamiin eri tapoihin ratkaista tavallisten differentiaaliyhtälöiden alkuarvotehtäviä. Nämä menetelmät toimivat johdantona ja vertailukohtana työssä esiteltäviin murtodifferentiaaliyhtälöiden numeerisiin ratkaisumenetelmiin, jotka johdetaan ja perustellaan yksityiskohtaisesti. Ratkaisumenetelmät tähän työhön on valikoitu siten, että niiden teoreettinen perusteleminen ei vaadi kohtuutonta määrää taustatietoja, mutta kuitenkin niin, että ne ovat käyttökelpoisia ja perustuvat kohtuullisen tuoreeseen tutkimukseen. Kannattaa kuitenkin huomata, että numeerisia ratkaisutekniikoita murtodifferentiaaliyhtälöille on paljon muitakin kuin tässä työssä esitetyt tavat. Vertailtaessa numeerisia ratkaisutekniikoita tavallisille differentiaaliyhtälöille ja murtodifferentiaaliyhtälöille havaittiin, että muisti-ilmiö on läsnä myös siellä ja kasvattaa tarvittavien laskutoimitusten määrää laskennan edetessä kauemmaksi lähtötilanteesta. Tässä tutkielmassa esiteltyjen menetelmien suoriutumista testataan muutamalla eri malliongelmalla ja suoriutumista mitataan tarkkuuden lisäksi myös nopeudella. Laskenta-algoritmit on ohjelmoitu osana tätä työtä ja ne ovat mukana työn liitteinä. Näiden algoritmien avulla tässä työssä tutkitaan menetelmien suorituskykyä niin tarkkuuden kuin nopeudenkin osalta. Menetelmien vertailu ja tulosten analysointi muodostavat keskeisen osan tätä työtä. Vertailussa käytetään neljää erilaista menetelmää eri askelpituuksilla ja menetelmiä sovelletaan useisiin erityyppisiin testiongelmiin. Saatujen tulosten perusteella voitiin tehdä muutamia erityisen tärkeitä havaintoja. Ensimmäinen merkittävä havainto oli ja on, että murtodifferentiaaliyhtälön kertaluvun kasvattaminen parantaa ratkaisevasti menetelmien tarkkuutta. Toinen tärkeä havainto tulosten perusteella oli, että pienillä muutoksilla algoritmeissa voidaan saavuttaa merkittäviä eroja nopeudessa. Kolmantena keskeisenä havaintona voitaneen pitää sitä, että menetelmien suppenemisnopeudet noudattivat varsin hyvin teoreettista mallia.Numerical methods for solving fractional differential equations. Abstract. A fractional differential equation is a differential equation involving derivatives with a non-integer order. These kind of equations can be useful when modelling phenomena with memory. If the system has a memory effect, not only the present situation affects to the later behaviour, but the history of the system as well. We familiarize ourselves with the basics of the theory and practise of the fractional differential equations in this work. The most known definitions and tools, that are also crucial for understanding the numerical algorithms, are presented. The most important definition presented, for this work and when dealing with the real life applications, is the Caputo derivative. The Caputo derivative allows to use natural initial conditions which is necessary when solving initial value problems with fractional derivatives. As an introduction to practise and numerical analysis of fractional differential equations, a couple of numerical methods for initial value problems of ordinary differential equations are given. These methods can be compared with and lead to the numerical methods for solving fractional differential equations presented in this work. These methods are justified with a detailed manner and they are applied to few model problems. The speed and precision of the methods for each of the problems were measured and the results are published in this work. The algorithms for the methods have been programmed as a part of this work and the source codes of these routines can be found as attachments

Modeling affirmative and negated action processing in the brain with lexical and compositional semantic models

Recent work shows that distributional semantic models can be used to decode patterns of brain activity associated with individual words and sentence meanings. However, it is yet unclear to what extent such models can be used to study and ecode fMRI patterns associated with specific aspects of semantic composition such as the negation function. In this paper, we apply lexical and compositional semantic models to decode fMRI patterns associated with negated and affirmative sentences containing hand-action verbs. Our results show reduced decoding (correlation) of sentences where the verb is in the negated context, as compared to the affirmative one, within brain regions implicated in action-semantic processing. This supports behavioral and brain imaging studies, suggesting that negation involves reduced access to aspects of the affirmative mental representation. The results pave the way for testing alternate semantic models of negation against human semantic processing in the brain

Program planning decisions in an external degree program: A case study

Some adult educators pursue a "grand" program planning model (Pennington & Green, 1976; Sork & Caffarella, 1990). Others question the applicability of any standard set of principles and procedures to all learning contexts (Cervero & Wilson, 1991; Brookfield, 1988). The purpose of this study was to explore this issue through a qualitative case study in which "planning in action" is documented in a single program and compared to models to determine which, if any of the models account for the processes and actions recorded.The target population of the study was university administrators, governmental administrators, continuing educators, faculty, and students. The context of the study is a university sponsored, external graduate program involving an institution of higher education, a governmental agency, and their respective subgroups.Data were collected through a qualitative process including interviews, participant observation, and document analysis. A modified dialectic hermeneutic process was followed to clarify issues and themes. Data were analyzed using a constant comparative method to develop a rich description of the case.Analysis led to a rich description of the case in both an historical and a present context. Four main themes emerged from the data, appropriateness of the use of institutional resources in the program, issues of program ownership and control, issues of quality, and elements directly related to program planning decisions.The study found that no single model nor any classification of models accounts for the myriad program planning activities and issues in this case. For example, individuals were proactive developers in contrast to the responsive role depicted in models. Developers used relationships and networks to build support and gather resources. Each of the stakeholders shared considerable decision making power. The process included the design of a reward structure for instructors and the sponsoring institution. The learner emphasis espoused by many models was not evident in this case.These findings suggest that program planning is an art rather than a science. Therefore, attempts to define a single, ideal process are not advised. Rather, the field should seek expanded understanding of the variety of approaches and processes that lead to effective program development

Comparing apples and oranges: assessment of the relative video quality in the presence of different types of distortions

<p>Abstract</p> <p>Video quality assessment is essential for the performance analysis of visual communication applications. Objective metrics can be used for estimating the relative quality differences, but they typically give reliable results only if the compared videos contain similar types of quality distortion. However, video compression typically produces different kinds of visual artifacts than transmission errors. In this article, we focus on a novel subjective quality assessment method that is suitable for comparing different types of quality distortions. The proposed method has been used to evaluate how well different objective quality metrics estimate the relative subjective quality levels for content with different types of quality distortions. Our conclusion is that none of the studied objective metrics works reliably for assessing the co-impact of compression artifacts and transmission errors on the subjective quality. Nevertheless, we have observed that the objective metrics' tendency to either over- or underestimate the perceived impact of transmission errors has a high correlation with the spatial and temporal activity levels of the content. Therefore, our results can be useful for improving the performance of objective metrics in the presence of both source and channel distortions.</p