Asteroseismology of Massive Stars : Some Words of Caution

Although playing a key role in the understanding of the supernova phenomenon, the evolution of massive stars still suffers from uncertainties in their structure, even during their "quiet" main sequence phase and later on during their subgiant and helium burning phases. What is the extent of the mixed central region? In the local mixing length theory (LMLT) frame, are there structural differences using Schwarzschild or Ledoux convection criterion? Where are located the convective zone boundaries? Are there intermediate convection zones during MS and post-MS phase, and what is their extent and location? We discuss these points and show how asteroseismology could bring some light on these questions.Comment: 10 pages, 5 figures, IAU Symposium 307, New windows on massive stars: asteroseismology, interferometry, and spectropolarimetry, G. Meynet, C. Georgy, J.H. Groh & Ph. Stee, ed

Intermediate range chemical ordering of cations in simple molten alkali halides

The presence of first sharp diffraction peaks in the partial structure factors is investigated in computer simulations of molten mixtures of alkali halides. An intermediate range ordering appears for the Li+ ions only, which is associated with clustering of this species and is not reflected in the arrangement of other ions. This ordering is surprising in view of the simplicity of the interionic interactions in alkali halides. The clustering reflects an incomplete mixing of the various species on a local length scale, which can be demonstrated by studying the complementary sub-space of cations in the corresponding pure alkali halides by means of a void analysis.Comment: 5 pages, 5 figure

Can an underestimation of opacity explain B-type pulsators in the SMC?

Slowly Pulsating B and $\beta$ Cephei are $\kappa$ mechanism driven pulsating B stars. That $\kappa$ mechanism works since a peak in the opacity due to a high number of atomic transitions from iron-group elements occurs in the area of $\log T \approx 5.3$. Theoretical results predict very few SPBs and no $\beta$ Cep to be encountered in low metallicity environments such as the Small Magellanic Cloud. However recent variability surveys of B stars in the SMC reported the detection of a significant number of SPB and $\beta$ Cep candidates. Though the iron content plays a major role in the excitation of $\beta$ Cep and SPB pulsations, the chemical mixture representative of the SMC B stars such as recently derived does not leave room for a significant increase of the iron abundance in these stars. Whilst abundance of iron-group elements seems reliable, is the opacity in the iron-group elements bump underestimated? We determine how the opacity profile in B-type stars should change to excite SPB and $\beta$ Cep pulsations in early-type stars of the SMC.Comment: 5 pages, 7 figures, to appear under electronic form in : Proceedings of the 4th HELAS International Conference: Seismological Challenges for Stellar Structur

The cytoplasmic domain of CD4 promotes the development of CD4 lineage T cells.

Thymocytes must bind major histocompatibility complex (MHC) proteins on thymic epithelial cells in order to mature into either CD8+ cytotoxic T cells or CD4+ helper T cells. Thymic precursors express both CD8 and CD4, and it has been suggested that the intracellular signals generated by CD8 or CD4 binding to class I or II MHC, respectively, might influence the fate of uncommitted cells. Here we test the notion that intracellular signaling by CD4 directs the development of thymocytes to a CD4 lineage. A hybrid protein consisting of the CD8 extracellular and transmembrane domains and the cytoplasmic domain of CD4 (CD884) should bind class I MHC but deliver a CD4 intracellular signal. We find that expression of a hybrid CD884 protein in thymocytes of transgenic mice leads to the development of large numbers of class I MHC-specific, CD4 lineage T cells. We discuss these results in terms of current models for CD4 and CD8 lineage commitment

High-pressure behaviour of GeO2: a simulation study

In this work we study the high pressure behaviour of liquid and glassy GeO2 by means of molecular dynamics simulations. The interaction potential, which includes dipole polarization effects, was parameterized from first-principles calculations. Our simulations reproduce the most recent experimental data to a high degree of precision. The proportion of the various GeOn polyhedra is determined as a function of the pressure: a smooth transition from tetrahedral to octahedral network is observed. Finally, the study of high-pressure, liquid germania confirms that this material presents an anomalous behaviour of the diffusivity as observed in analog systems such as silica and water. The importance of penta-coordinated germanium ions for such behaviour is stressed.Comment: 16 pages, 4 figures, accepted as a Fast Track Communication on Journal of Physics: Condensed Matte

Combining social network analysis and the NATO Approach Space to define agility. Topic 2: networks and networking

This paper takes the NATO SAS-050 Approach Space, a widely accepted model of command and control, and gives each of its primary axes a quantitative measure using social network analysis. This means that the actual point in the approach space adopted by real-life command and control organizations can be plotted along with the way in which that point varies over time and function. Part 1 of the paper presents the rationale behind this innovation and how it was subject to verification using theoretical data. Part 2 shows how the enhanced approach space was put to use in the context of a large scale military command post exercise. Agility is represented by the number of distinct areas in the approach space that the organization was able to occupy and there was a marked disparity between where the organization thought it should be and where it actually was, furthermore, agility varied across function. The humans in this particular scenario bestowed upon the organization the levels of agility that were observed, thus the findings are properly considered from a socio-technical perspective

Are the stars of a new class of variability detected in NGC~3766 fast rotating SPB stars?

A recent photometric survey in the NGC~3766 cluster led to the detection of stars presenting an unexpected variability. They lie in a region of the Hertzsprung-Russell (HR) diagram where no pulsation are theoretically expected, in between the $\delta$ Scuti and slowly pulsating B (SPB) star instability domains. Their variability periods, between $\sim$0.1--0.7~d, are outside the expected domains of these well-known pulsators. The NCG~3766 cluster is known to host fast rotating stars. Rotation can significantly affect the pulsation properties of stars and alter their apparent luminosity through gravity darkening. Therefore we inspect if the new variable stars could correspond to fast rotating SPB stars. We carry out instability and visibility analysis of SPB pulsation modes within the frame of the traditional approximation. The effects of gravity darkening on typical SPB models are next studied. We find that at the red border of the SPB instability strip, prograde sectoral (PS) modes are preferentially excited, with periods shifted in the 0.2--0.5~d range due to the Coriolis effect. These modes are best seen when the star is seen equator-on. For such inclinations, low-mass SPB models can appear fainter due to gravity darkening and as if they were located between the $\delta$~Scuti and SPB instability strips.Comment: 6 pages, 2 figures, to appear in the proceedings of the IAU Symposium 307, New windows on massive stars: asteroseismology, interferometry, and spectropolarimetr

Determining the metallicity of the solar envelope using seismic inversion techniques

The solar metallicity issue is a long-lasting problem of astrophysics, impacting multi- ple fields and still subject to debate and uncertainties. While spectroscopy has mostly been used to determine the solar heavy elements abundance, helioseismologists at- tempted providing a seismic determination of the metallicity in the solar convective enveloppe. However, the puzzle remains since two independent groups prodived two radically different values for this crucial astrophysical parameter. We aim at provid- ing an independent seismic measurement of the solar metallicity in the convective enveloppe. Our main goal is to help provide new information to break the current stalemate amongst seismic determinations of the solar heavy element abundance. We start by presenting the kernels, the inversion technique and the target function of the inversion we have developed. We then test our approach in multiple hare-and-hounds exercises to assess its reliability and accuracy. We then apply our technique to solar data using calibrated solar models and determine an interval of seismic measurements for the solar metallicity. We show that our inversion can indeed be used to estimate the solar metallicity thanks to our hare-and-hounds exercises. However, we also show that further dependencies in the physical ingredients of solar models lead to a low accuracy. Nevertheless, using various physical ingredients for our solar models, we determine metallicity values between 0.008 and 0.014.Comment: Accepted for publication in MNRA

Aplikasi Pengelolaan Data Praktikum Laboratorium Komputer STMIK Widya Cipta Dharma Berbasis Intranet

UPT. Laboratorium komputer STMIK Widya Cipta Dharma merupakan sebuah unit kerja yang memberikan pelayanan akademik. Laboratorium Komputer mempunyai fungsi sebagai tempat proses pembelajaran. Dalam kegiatan praktikum pada laboratorium komputer mahasiswa menggunakan komputer tetap dalam praktikum mata kuliah tersebut karena data-data praktikum hanya ada pada komputer tersebut tanpa mempunyai penyimpanan data yang baik. Apabila mahasiswa maupun dosen ingin meminta data-data tersebut meraka harus menghubungi admin laboratorium tersebut mendapatkan data-data praktikum tersebut lalu membuka komputer mahasiswa tersebut untuk disalin data-datanya. Hal ini tidak efisien dalam melakukan pertukaran data ditambah komputer digunakan oleh banyak mahasiswa membuat data -data praktikum menumpuk dan dapat tercampur dengan data mahasiswa lain. Penelitian ini dibuat untuk mengatasi berbagai kendala yang dihadapi oleh Laboratorium Komputer STMIK WICIDA. Dalam membangun aplikasi ini menggunakan metode pengembangan sistem waterfall, metode pengujian blackbox dan pengujian beta, database MYSQL dan menggunakan bahasa pemrograman PHP (PHP Hypertext Preprocessor), dreamweaver sebagai webeditor, apache sebagai webserver local, flowchart, Data Flow Diagram dan Entity Relationship Diagram sebagai alat bantu perancangan sistem. Dengan adanya aplikasi pengelolaan data praktikum berbasis intranet ini diharapkan dapat membantu laboratorium komputer STMIK WICIDA dan memberikan kemudahan dalam pengelolaan data praktikum

Adoption and Influence: Industry Evaluation of the GrassGro\u3csup\u3eTM\u3c/sup\u3e Decision Support Tool

The GrassGro Decision Support tool (DS tool) (Donnelly and Moore, 1999) was released for commercial use in Australia with a training package in late 1997. An assessment of its adoption was made by a survey of 53 registered users in March 1999. An evaluation of the software and training package was made at training workshops by 92 users between 1997 and December 1999. The response rates to the survey and the evaluation were 62% and 82% respectively. Seventy six percent of survey respondents had analysed at least one problem with GrassGro and 27% had applied GrassGro to five or more problems encountered in the management of grazing enterprises. Users valued training highly and on completion were confident in their use of GrassGro; 63% of repondents had extrapolated the results of their analyses to a district or regional level