Variability of stellar granulation and convective blueshift with spectral type and magnetic activity. I. K and G main sequence stars

In solar-type stars, the attenuation of convective blueshift by stellar magnetic activity dominates the RV variations over the low amplitude signal induced by low mass planets. Models of stars that differ from the Sun will require a good knowledge of the attenuation of the convective blueshift to estimate its impact on the variations. It is therefore crucial to precisely determine not only the amplitude of the convective blueshift for different types of stars, but also the dependence of this convective blueshift on magnetic activity, as these are key factors in our model producing the RV. We studied a sample of main sequence stars with spectral types from G0 to K2 and focused on their temporally averaged properties: the activity level and a criterion allowing to characterise the amplitude of the convective blueshift. We find the differential velocity shifts of spectral lines due to convection to depend on the spectral type, the wavelength (this dependence is correlated with the Teff and activity level), and on the activity level. This allows us to quantify the dependence of granulation properties on magnetic activity for stars other than the Sun. The attenuation factor of the convective blueshift appears to be constant over the considered range of spectral types. We derive a convective blueshift which decreases towards lower temperatures, with a trend in close agreement with models for Teff lower than 5800 K, but with a significantly larger global amplitude. We finally compare the observed RV variation amplitudes with those that could be derived from our convective blueshift using a simple law and find a general agreement on the amplitude. Our results are consistent with previous results and provide, for the first time, an estimation of the convective blueshift as a function of Teff, magnetic activity, and wavelength, over a large sample of G and K main sequence stars

On the expressive power of read-once determinants

We introduce and study the notion of read-$k$ projections of the determinant: a polynomial $f \in \mathbb{F}[x_1, \ldots, x_n]$ is called a {\it read-$k$ projection of determinant} if $f=det(M)$, where entries of matrix $M$ are either field elements or variables such that each variable appears at most $k$ times in $M$. A monomial set $S$ is said to be expressible as read-$k$ projection of determinant if there is a read-$k$ projection of determinant $f$ such that the monomial set of $f$ is equal to $S$. We obtain basic results relating read-$k$ determinantal projections to the well-studied notion of determinantal complexity. We show that for sufficiently large $n$, the $n \times n$ permanent polynomial $Perm_n$ and the elementary symmetric polynomials of degree $d$ on $n$ variables $S_n^d$ for $2 \leq d \leq n-2$ are not expressible as read-once projection of determinant, whereas $mon(Perm_n)$ and $mon(S_n^d)$ are expressible as read-once projections of determinant. We also give examples of monomial sets which are not expressible as read-once projections of determinant

Spin Gaps in High Temperature Superconductors

The phenomenology and theory of spin gap effects in high temperature superconductors is summarized. It is argued that the spin gap behavior can only be explained by a model of charge 0 spin 1/2 fermions which become paired into singlets and that there are both theoretical and experimental reasons for believing that the pairing is greatly enhanced in the bilayer structure of the $YBa_2Cu_3O_{6+x}$ system. This article will appear in the Proceedings of the Stanford Conference on Spectroscopies in Novel Superconductors. To obtain postscript files containing the figures send mail to [email protected]: 9 pages, revtex. To obtain figures contact [email protected]

Negotiations of minority ethnic rugby league players in the Cathar country of France

This article is based on new empirical, qualitative research with minority ethnic rugby league players in the southwest of France. Drawing on similar research on rugby league in the north and the south of England, the article examines how rugby league, traditionally viewed as a white, working-class male game (Collins, 2006; Denham, 2004; Spracklen, 1995, 2001) has had to re-imagine its symbolic boundaries as they are constituted globally and locally to accommodate the needs of players from minority ethnic backgrounds. In particular, the article examines the sense in which experiences of minority ethnic rugby league players in France compare with those of their counterparts in England (Spracklen, 2001, 2007), how rugby league is used in France to construct identity, and in what sense the norms associated with the imaginary community of rugby league are replicated or challenged by the involvement of minority ethnic rugby league players in France. Questions about what it means to be (provincial, national) French (Kumar, 2006) are posed, questions that relate to the role of sport in the construction of Frenchness, and in particular the role of rugby league (and union). © Copyright ISSA and SAGE Publications

Magnetic frustration in a stoichiometric spin-chain compound, Ca3_3CoIrO6_6

The temperature dependent ac and dc magnetization and heat capacity data of Ca$_3$CoIrO$_6$, a spin-chain compound crystallizing in a K$_4$CdCl$_6$-derived rhombohedral structure, show the features due to magnetic ordering of a frustrated-type below about 30 K, however without exhibiting the signatures of the so-called "partially disordered antiferromagnetic structure" encountered in the isostructural compounds, Ca$_3$Co$_2$O$_6$ and Ca$_3$CoRhO$_6$. This class of compounds thus provides a variety for probing the consequences of magnetic frustration due to topological reasons in stoichiometric spin-chain materials, presumably arising from subtle differences in the interchain and intrachain magnetic coupling strengths. This compound presents additional interesting situations in the sense that, ac susceptibility exhibits a large frequency dependence in the vicinity of 30 K uncharacteristic of conventional spin-glasses, with this frustrated magnetic state being robust to the application of external magnetic fields.Comment: Physical Review (Rapid Communications), in pres

Downregulating Notch counteracts KrasG12D-induced ERK activation and oxidative phosphorylation in myeloproliferative neoplasm.

The Notch signaling pathway contributes to the pathogenesis of a wide spectrum of human cancers, including hematopoietic malignancies. Its functions are highly dependent on the specific cellular context. Gain-of-function NOTCH1 mutations are prevalent in human T-cell leukemia, while loss of Notch signaling is reported in myeloid leukemias. Here, we report a novel oncogenic function of Notch signaling in oncogenic Kras-induced myeloproliferative neoplasm (MPN). We find that downregulation of Notch signaling in hematopoietic cells via DNMAML expression or Pofut1 deletion significantly blocks MPN development in KrasG12D mice in a cell-autonomous manner. Further mechanistic studies indicate that inhibition of Notch signaling upregulates Dusp1, a dual phosphatase that inactivates p-ERK, and downregulates cytokine-evoked ERK activation in KrasG12D cells. Moreover, mitochondrial metabolism is greatly enhanced in KrasG12D cells but significantly reprogrammed by DNMAML close to that in control cells. Consequently, cell proliferation and expanded myeloid compartment in KrasG12D mice are significantly reduced. Consistent with these findings, combined inhibition of the MEK/ERK pathway and mitochondrial oxidative phosphorylation effectively inhibited the growth of human and mouse leukemia cells in vitro. Our study provides a strong rational to target both ERK signaling and aberrant metabolism in oncogenic Ras-driven myeloid leukemia

Mathematical modelling in animal nutrition: a centenary review

A centenary review presents an opportunity to ponder over the processes of concept development and give thought to future directions. The current review aims to ascertain the ontogeny of current concepts, underline the connection between ideas and people and pay tribute to those pioneers who have contributed significantly to modelling in animal nutrition. Firstly, the paper draws a brief portrait of the use of mathematics in agriculture and animal nutrition prior to 1925. Thereafter, attention turns towards the historical development of growth modelling, feed evaluation systems and animal response models. Introduction of the factorial and compartmental approaches into animal nutrition is noted along with the particular branches of mathematics encountered in various models. Furthermore, certain concepts, especially bioenergetics or the heat doctrine, are challenged and alternatives are reviewed. The current state of knowledge of animal nutrition modelling results mostly from the discernment and unceasing efforts of our predecessors rather than serendipitous discoveries. The current review may stimulate those who wish for greater understanding and appreciation